Officials at the Federal Reserve, under pressure from President Trump to restart interest rate cuts after an extended pause, say they are prepared to lower borrowing costs if the labor market weakens.

But Mr. Trump’s own immigration policies risk making it much harder for those policymakers to know whether that is happening, putting a divided central bank in an even more fraught position as it debates when and by what magnitude to lower borrowing costs.

The Trump administration in recent months has moved to revoke the legal status of hundreds of thousands of immigrants and has conducted high-profile immigration raids at work sites in Los Angeles and other cities. It has stepped up security at the U.S.-Mexican border and has publicly threatened to deport as many as a million workers a year.

The full effect of those policies is not yet clear. But virtually all analysts expect the immigrant population to grow much more slowly this year, and perhaps even to fall. That could leave employers who rely on immigrant labor scrambling to fill positions, potentially pushing up wages and causing shortages of certain goods or services.

A shrinking immigrant labor force could pose a big problem for the Fed, making it harder to tell whether a slowdown in job growth is the result of falling demand for workers, fewer available employees or both. The shrinking pool of workers could also present another source of inflationary pressures beyond tariffs that officials would have to navigate.

“The Fed is in a challenging position,” said Betsey Stevenson, a former chief economist at the Labor Department who is now a professor at the University of Michigan. “They need to be really careful that what they’re seeing is actually weak labor demand and not contracting labor supply caused by Trump’s policies, and that’s tricky.”

The Labor Department on Thursday will release its monthly snapshot of hiring and unemployment, which is expected to show a continued, gradual cool-down in the pace of job growth. Many forecasters expect a further, perhaps sharper decline in hiring in the second half of the year.

Ordinarily, such a slowdown — at least, if accompanied by moderate inflation — would be a clear signal to the Fed to begin lowering borrowing costs to stimulate demand and head off a recession. But this time, a moderation may simply reflect slower growth in the labor force.

“Our sense of whether a monthly jobs number is good or bad needs to adjust,” said Jed Kolko, an economist who served in the Commerce Department during the Biden administration.

A Fuzzy Target

In gauging the health of the job market, economists typically compare monthly payroll figures with the “break-even” pace of hiring: the theoretical level of monthly job growth that is just enough to keep up with growth in the labor force.

Anything below this break-even rate will cause the unemployment rate to rise, as people entering the labor force struggle to find jobs. Job growth above that point will cause the unemployment rate to fall. If job growth remains above the break-even rate for long enough, companies will have to compete for a dwindling supply of available workers, risking faster wage growth and, ultimately, higher inflation.

The break-even rate can shift over time in response to demographic patterns, like the aging of the baby boom generation, or societal trends, like rising college attendance. In recent years, however, it has moved around much more than usual, first in response to the coronavirus pandemic — which temporarily pushed tens of millions of people out of the labor force — and then to big swings in immigration.

In the years before the pandemic, most estimates put the break-even rate at around 100,000 jobs per month. That figure ballooned to perhaps 200,000 during the immigration boom early in President Biden’s term, allowing employers to keep adding jobs at a rapid pace long after many forecasters had expected the country to begin running out of available workers.

Now, pretty much every economist agrees that the break-even rate is lower, and will fall further as Mr. Trump’s immigration policies take full effect. But precise estimates vary widely, from as few as 50,000 jobs per month to as many as 150,000.

That means that if this week’s Labor Department report meets forecasters’ expectations of a gain of roughly 110,000 jobs, economists will not agree on whether that exceeds the break-even rate.

“It’s just really hard to take payroll growth as a reliable signal of the health of the economy anymore,” said Ernie Tedeschi, director of economics at the Yale Budget Lab.

Looking for Other Evidence

As a result, Mr. Tedeschi and other economists said, they pay less attention to monthly job growth and focus more on the unemployment rate, which offers a more direct measure of whether there are enough jobs for all the workers who want them.

“The unemployment rate will end up being a much more useful measure,” said Wendy Edelberg, an economist at the Brookings Institution who has studied the impact of immigration on economic data.

Economists will also be paying attention to other measures, including the number of job openings, the applications for unemployment insurance and the rate at which workers quit their jobs. Many will also be watching for signs that wage growth is picking up, which would indicate that the labor market is heating up, even if job growth is slowing.

But those indicators are also imperfect. The unemployment rate is based on a monthly survey of households that is generally viewed as less reliable than the much larger survey of businesses that is the source of payroll figures. The most reliable wage numbers are released only four times a year. And the different measures often tell conflicting stories, especially over short periods.

That raises the risk that Fed officials will disagree about how to interpret the job market’s signals. And even if they do reach a consensus, they could have a hard time communicating their thinking to investors and the public, said Matthew Luzzetti, chief U.S. economist at Deutsche Bank.

“I have been worried that it’s possible there could be some gap between the Fed’s perception of what is a good jobs report and what the market’s perception on what a good job report is,” he said.

Politics and Division

Political pressures will only add to the Fed’s challenges.

Mr. Trump has subjected Jerome H. Powell, the Fed chair, to an onslaught of attacks in recent months for not acquiescing to his demands to lower borrowing costs. On Monday, Mr. Trump penned him a handwritten note accusing the Fed of costing the country a “fortune.”

Mr. Powell has so far shrugged off these attacks, saying the labor market remains strong even as demand for workers has gradually cooled.

“The labor market is not crying out for a rate cut,” he told reporters after the most recent policy decision in June, when the central bank voted unanimously to hold interest rates steady for a fourth straight meeting.

Speaking to lawmakers roughly a week later, he said that while the Fed did not currently see weakness in the labor market, “if we did, that would change things.”

But fissures between officials have already started to emerge. While the bulk of the Fed’s policymakers have endorsed the central bank’s wait-and-see approach to further interest rate cuts — with many projecting no reductions this year — two Trump appointees have recently made the case for a move as early as this month.

If job growth declines further, pressure to cut rates will almost certainly intensify. But if the slowdown is the result of reduced immigration, rather than reduced demand for labor, such a move could be a mistake, leading to an increase in inflation, some economists warn.

“If they see monthly payroll employment growth slow a lot, their first thought should be that probably reflects a big decline in labor supply and so it’s not on the face of it signaling that we’re in recession or about to enter recession,” Ms. Edelberg said.

In a report published on Wednesday by the American Enterprise Institute, Ms. Edelberg and two co-authors estimated that the break-even pace of job growth could fall as low as 10,000 jobs per month by the end of the year. That suggests that job growth is all but certain to decline significantly in coming months. But Ms. Edelberg said many Americans — and even many economists — were still likely to be alarmed by the slowdown.

“Good luck with telling people that a payroll growth figure of 30,000 is nothing to be worried about,” she said.

Weighing heavily on the Fed is the mistake officials made in the aftermath of the pandemic, when they underestimated the severity of the price pressures stemming from the global economic shutdown and inflation soared to the highest level in roughly four decades.

Inflation has since moderated but has yet to return to the Fed’s 2 percent target. And Mr. Trump’s policies on both trade and immigration have stoked anxiety that inflation will accelerate again.

Letting inflation get out of control again is a “bigger mistake” than causing the economy to slow a bit too much, said Seth Carpenter, a former Fed economist who is now at Morgan Stanley. The Fed can always play catch-up by lowering interest rates more aggressively, he said.

Mr. Carpenter expects a cooling economy to lead to less demand for labor, pushing up unemployment even as the supply of workers also ebbs. Still, he expects the Fed to stay on hold for the remainder of the year before lowering borrowing costs more significantly throughout 2026.

Ms. Stevenson warned that the Fed’s credibility was on the line if it ended up having to flip-flop on its policy decisions — for example, lowering interest rates in September only to raise them again six months later.

“If you can see the potential to move in either direction, just wait for more data,” she said.