Immigrants made up almost 90 percent of the United States' labor market growth over the past five years, according to a report that is raising concerns about former President Donald Trump's mass deportation plans.

The National Foundation for American Policy (NFAP) said 3.6 million foreign workers entered the U.S. job market between 2019 and 2024, compared to 479,000 American-born workers.

While the Republican presidential nominee's focus for mass deportation has been on alleged criminals, the target to remove millions was again met with skepticism by the NFAP.

"The reality is that most of the people who would end up getting deported in any sort of mass deportation are people who are simply working in the U.S. labor force," Stuart Anderson, NFAP executive director, told Newsweek. "In fact, what is likely to happen is there will not there will not be an emphasis on removing criminals, but an emphasis on removing everyone to drive up the numbers to reach quotas."

Anderson said it was likely that those who had worked in the U.S. for a decade or more would be removed, meaning a loss of "productive labor," leading to increased inflation and a drop in GDP.

Responding to the report, the Trump campaign pointed the finger at the current administration.

"Kamala Harris and Joe Biden have built back broke, losing 34,000 manufacturing jobs in just the past two months as foreign countries benefit from Harris' weak economic policies, and Harris' open border policies have destroyed 825,000 jobs for native-born Americans while 1.2 million foreign-born workers gained employment," Karoline Leavitt, the Trump campaign's national press secretary, told Newsweek in a statement.

Immigration experts have denounced claims that migrants have stolen jobs, telling Newsweek in July and August that there simply are not enough American workers to fill the number of job openings.

"High-skilled immigration has contributed a lot to U.S. entrepreneurship, innovation and the labor market, because these people generate growth of firms and job numbers," Giovanni Peri, an economist at the University of California, previously told Newsweek.

Those working in the farm industry also said that large-scale deportation could dramatically cut the number of workers available, while advocates have warned about deporting potential workers.

Anderson said the NFAP report highlighted a major issue facing the U.S. if the migrant workforce was reduced -- that American-born citizens were not likely to be able to fill the gap.

"If you look over the past five years, without immigrants and their children, there would have been no labor force growth in the United States," he said. "And that means that without labor force growth, it's very difficult for a country to have economic growth, and without economic growth, living standards in a country stagnate and potentially even decline."

Part of the reason, as reported earlier in the year, is that the U.S. population is aging out of the workforce, but fewer Americans have been having children, meaning less entering the workforce.

NFAP predicts that the total number of American-born workers will peak in 2052, at 146.7 million, after which immigrant workers will be the only source of growth.

Those coming to work in the U.S. are not just farmhands or construction workers but those in health care, technology and finance who require visas to be able to either stay after college or enter the U.S. for a job.

The report points to a push for increased manufacturing of semiconductors in the country for use in microchips, but that less than 30 percent of full-time electrical engineering graduate students are U.S. citizens, so foreign students are needed, too.

"It wouldn't make a lot of sense, if people receive a certain level of education and have a certain desire to go in a certain fields, why should they work in agriculture in the fields, work on top of a roof in a dangerous job working construction and try to fill other jobs, when there are other people who are happy to fill those jobs and fill niches in the labor market?" Anderson said.

"Particularly when you look at immigrants who come in and are able to care for children or elders, that frees up, typically, professional women to be able to work and use their education to their fullest extent."

Vice President Harris, the Democratic presidential nominee, has promised to increase legal pathways for migrants, which advocates have said would then cut illegal border crossings, which both candidates have said they want to achieve.

Polling by the Pew Research Center this month showed supporters of both candidates were united on strengthening border security and increasing highly skilled immigration.