In an effort to further curtail the number of immigrants living in the United States, the Trump administration is considering a proposal that would drastically increase barriers for immigrants seeking United States citizenship or legal residency who have used several types of public benefits, including the Affordable Care Act.

The move, which is expected to be announced shortly, according to NBC News, would not need Congressional approval and could affect immigrants who have previously used Supplemental Nutrition Assistance Program (SNAP), the Children’s Health Insurance Program (CHIP) and Obamacare.

Details of the proposal, drafted by White House advisor Stephen Miller, are still being finalized. But a draft of the plan, obtained by The Washington Post several months ago, would broaden the definition of public benefits.

Whereas the government already bars some immigrants who receive cash welfare payments from obtaining citizenship or legal residency, under the new proposal those exclusions would be extended to a wider population, penalizing immigrants who use commonly claimed earned-income tax credit and health insurance subsidies.

Immigration experts say the proposal could affect up to 20 million immigrants, amounting to the largest transformation of the United States immigration system in decades.

“We’ve seen abuses like this before in our history—whether it was turning away Jews fleeing the Holocaust or discriminating against Irish Catholics,” advocacy group National Immigration Law Center said in a statement. “We know that Trump is dead set on harming immigrants—whether it be taking away children from their parents, ending the #DACA program for 800,000 Dreamers, or rigging the system for the rich.”

The Department of Homeland Security, in a statement to NBC News, said: “The administration is committed to enforcing existing immigration law, which is clearly intended to protect the American taxpayer by ensuring that foreign nationals seeking to enter or remain in the U.S are self-sufficient.”

Recent studies have illustrated that U.S. immigrants are less likely than native-born residents to use public welfare programs and health care services.

A May study from the libertarian Cato Institute found that immigrants use 39 percent fewer public welfare benefits than U.S. natives, mostly because they are less likely to use Social Security benefits and Medicare.

Another study, published today (August 8) in the International Journal of Health Services, finds that immigrants’ expenditures on health care were between one half and two thirds the rate of U.S.-born residents. And immigrants, the study found, paid more toward medical expenses than they withdrew.

In light of these studies, and the Trump administration’s multi-pronged attacks on immigrants, immigration advocates framed the new White House proposal as a politically-driven, racist assault.

“Trump and Miller will keep pointing the finger at immigrants, picking fights with African Americans and trash-talking powerful women because they believe they can channel anger over stagnant wages, rising healthcare costs and threats to retirement security into fear and loathing of their so-called ‘other,’” tweeted Frank Sharry, executive director of immigrant advocacy group America’s Voice.