More than 2 million new immigrants have arrived to take jobs in the U.S. since 2019, according to a new study released Thursday that challenges a growing chorus of voices arguing the country needs still more immigrants to keep the economy humming.

The Center for Immigration Studies, a think tank that advocates for stricter immigration controls, said the lack of willing workers isn’t a matter of immigration but rather a result of native-born Americans dropping out of the labor pool altogether.

Some 1.9 million fewer Americans are in the workforce now compared to before the pandemic, the researchers said, citing the U.S. Census Bureau’s Current Population Survey data.

“This decline is a disaster for the economy and more important for society as being out of the labor force is associated with numerous problems including crime, drug abuse and even an early death,” said Steven A. Camarota, the lead author of the new study.

Immigration advocates and some business groups have argued that the U.S. is facing a dearth of immigrant workers after the pandemic. They say travel restrictions sapped the economy of newcomers that should be here holding down jobs.

Mr. Camarota’s work disputes that notion of “missing” immigrants.

At the end of 2019, or just before the pandemic, there were 27.4 million immigrants — here legally and illegally — holding jobs in the U.S.

That figure dipped during the early days of the pandemic, with just 25.3 million in jobs at the end of 2020. But it came roaring back in 2021, reaching 27.6 million, and soared to 29.4 million at the end of last year — an increase of 2 million over the pre-pandemic figure.

It also represents a surge of 4 million immigrants in the two years of the Biden administration, which has seen an unprecedented run at the U.S.-Mexico border.

Mr. Camarota’s numbers come just days after a new Gallup poll found Americans souring on the benefits of immigration. Just 8% of those surveyed said they want to see more immigration, while 40% said they want to see less.

That reverses a trend during the last administration, when President Donald Trump’s stance on immigration seemed to invite a backlash of public opinion as Americans embraced immigration as a rebuff of the president.

“Amid news of the migrant surge along the border with Mexico and the humanitarian and political problems arising from it, Americans across the political spectrum have grown less content with the level of U.S. immigration in recent years,” Gallup said.