Early evidence suggests that White House policy is reducing the size of the immigrant labor force, in turn contributing to a recent drawdown in the overall U.S. labor pool, according to several economists.

CNBC spoke with a range of economists from financial firms, economic research institutions and think tanks, and also reviewed recent research notes and analyses that economists have published on immigration and the job market.

If a reduction in the immigrant labor force is sustained, such a trend would be a concern for the U.S. economy, those experts have said or written.

That’s because the economy will increasingly rely on immigrants to fuel population and labor force growth given demographic trends among the U.S.-born populace, like retirements among baby boomers and lower fertility rates, they said.

The downward shift in the immigrant labor force in recent months is “definitive,” said Mark Zandi, chief economist at Moody’s.