(CNN) The Trump administration is seeking to give itself broad latitude to reject immigrants from the US if they have too little income and education, which could effectively impose a merit-based immigration system without an act of Congress.

The change is put forth in a proposed regulation , which would dramatically reshape how the government defines an immigrant likely to be dependent on the government.

President Donald Trump has long touted what he calls a merit-based system of immigration, backing a legislative proposal that would have heavily favored English-speaking, highly educated and high-earning immigrants over lower-skilled and lower-income applicants.

Quietly announced Saturday night, the proposed regulation could give the administration the authority to reshape the population of US immigrants in that direction without legislation.

The rule would mean many green card and visa applicants could be turned down if they have low incomes or little education because they'd be deemed more likely to need government assistance -- such as Medicaid or food stamps -- in the future.

The proposal applies to those looking to come to the US and those already here looking to extend their stay. And even if immigrants decide not to use public benefits they may be eligible for, the government could, under the proposed rule, still decide they are likely to do so "at any time in the future" and thus reject them from the US.

The administration says the proposed revamp of the so-called public charge rule is designed to ensure immigrants can support themselves financially.

"This proposed rule will implement a law passed by Congress intended to promote immigrant self-sufficiency and protect finite resources by ensuring that they are not likely to become burdens on American taxpayers," Department of Homeland Security Secretary Kirstjen Nielsen said Saturday.

But immigration advocates say it goes far beyond what Congress intended and will discriminate against those from poorer countries, keep families apart and prompt legal residents to forgo needed public aid, which could also impact their US citizen children.

They also say it will penalize even hard-working immigrants who only need a small bit of temporary assistance from the government.

"(The proposed rule) would radically reshape our legal immigration system, putting the wealthy at the front of the line, ahead of hardworking families who have waited years to reunite," a coalition of more than 1,100 community advocacy groups wrote in a statement this week. "No longer would the US be a beacon for the world's dreamers and strivers. Instead, America's doors would be open only to the highest bidder."

How does it work now?

The "public charge" provision dates back at least to the Immigration Act of 1882. Federal lawmakers at the time wanted to make sure that immigrants would be able to take care of themselves and not end up a public burden.

Under current regulations put in place in 1996, the term is defined as someone who is "primarily dependent" on government assistance, meaning it supplies more than half their income.

But it only counted cash benefits, such as Temporary Assistance for Needy Families or Supplemental Security Income from Social Security.

Immigration officials can take into account an applicant's financial resources, health, education, skills, family status and age. But few people are rejected on these relatively narrow grounds, experts said.

How would the rule change?

The Trump administration would expand the public charge concept to include more widely used benefits, including Medicaid, food stamps, housing assistance and the Medicare drug subsidy for low-income seniors.

It would also vastly expand what's considered a "public charge," moving beyond "primary dependence" to anyone who accepts the equivalent of at least 15% of federal poverty guidelines. Under current levels, that would equate to roughly $1,800 a year, or $150 a month in assistance.

In the proposal, DHS says it believes anyone who receives that much assistance "is neither self-sufficient nor on the road to achieving self-sufficiency."

And the rule would evaluate applicants on the probability that they would ever enroll in one or more of these assistance programs -- even if they don't currently.

This wouldn't lead to automatic rejections, but would be considered negative factors in a complex formula. For instance, having an income below 125% of the poverty level (roughly $15,200 for an individual or $31,400 for a family of four) would be a negative factor, as would having a large family or being over age 65. But earning more than 250% of the poverty level (about $30,350 for an individual or $62,750 for a family of four) would be a strongly positive factor.

Medical conditions could also be taken into account. The system would give immigration officers a lot of discretion in determining whether people who are sick or have pre-existing conditions would be able to purchase their own health insurance, rather than apply for Medicaid, for instance, or whether large families would be able to buy their own food without turning to the Supplemental Nutrition Assistance Program, the official name for food stamps.

"It's more about: Is your current income ... something that makes you likely to apply for benefits in the future," said Shawn Fremstad, senior fellow at the left-leaning Center for American Progress.

Who would be affected?

The draft regulation would include anyone seeking to come to the US on various visas, with a few exceptions for immigrants like refugees. It would also hit those already in the country who are seeking to become permanent legal residents or extend their stay by renewing their status.

The population expected to be most impacted is those still outside the US, experts say, but the rule estimates nearly 400,000 immigrants already in the US per year would be subject to the new scrutiny.

The new rules would also have an impact on families, making it much harder for naturalized citizens and legal residents to sponsor family members from low-income countries, such as Mexico or China, Fremstad said.

"The proposed rule would single out legal immigrants who use just a small amount of benefits and punish those who are hard-working," said Theresa Cardinal Brown, director of immigration and cross-border policy at the Bipartisan Policy Center, which advocates for policies it says stand the test of research.

"While immigrants use benefits at lower rates than Americans overall, this rule would penalize hard-working immigrants who use even just a few dollars in benefits over a relatively short period to cover a one-time need," Brown said. "That's not most people's definition of a 'public charge.'"

Supporters of the proposed rule, however, say that it will protect Americans from having to support low-income, low-skilled immigrants.

"Immigrants with a high school diploma or less impose a significant burden on taxpayers," said Robert Rector, a senior research fellow at the conservative Heritage Foundation, noting that there are millions of people who want to move to the United States who won't be a financial drain.

What about undocumented immigrants?

Undocumented immigrants are largely ineligible for public assistance so they generally would not be affected, unless an avenue opens up for them to apply for green cards or visas.

What about US citizen children?

Unlike a leaked draft of an earlier version of the regulation, these regulations would not apply to benefits used by US citizen children.

How will the proposed rule affect those who already have green cards?

The overhaul shouldn't have an impact on permanent legal residents, who generally have to wait five years before they can apply for benefits anyway. The public charge rule is not considered when green card holders are applying for citizenship.

But advocates are worried that it would have a chilling effect. Fear and misinformation could prompt some residents who are entitled to benefits to withdraw from the programs, experts say. The Trump administration's aggressive immigration policies are already causing this to happen.

The rule notes that a number of consequences could stem from the rule, including that high numbers of immigrants stop using assistance.

According to the administration, the rule could result in "increased prevalence of obesity and malnutrition, especially for pregnant or breastfeeding women, infants, or children;" people using emergency rooms as their primary health care; more communicable diseases due to lower vaccination rates; higher levels of poverty and uncertain housing, and "reduced productivity and educational attainment."

Does using benefits make you dependent on government?

This is a long-standing and hotly contested question.

Conservatives say that America's safety net has become so large and generous that it's hard to escape. More than 70 million people receive Medicaid and 39.5 million are on food stamps, the largest programs in the system.

That's why Republicans are pushing to add work requirements to various programs. They argue that mandating that people work will lead to self-sufficiency and get them off the rolls.

Left-leaning experts, however, say that public assistance programs are crucial to help those going through temporary hard times and to support people who work but don't make enough to survive on their own.

Take Medicaid, which covers roughly 1 in 5 Americans. Some 43% are children and about 25% are elderly or disabled, according to the Kaiser Family Foundation.

The majority of the roughly 25 million non-disabled, non-elderly adults on Medicaid have jobs. Some 42% work full-time, while another 18% hold part-time positions, the foundation found.

Many people cycle in and out of public assistance during their lifetimes.

By age 60, nearly 45% of American adults have used the safety net, according to a 2014 book by social scientists Mark Robert Rank, Thomas Hirschl and Kirk Foster. But most received benefits for only a few years.

When will this take effect?

The rule is only a proposal. Once it is published in the Federal Register, there will be 60 days for the public to submit comments. The Department of Homeland Security is then required by law to review the comments and address substantive ones before proposing the final rule.

Even then, it is likely to face legal challenges. California Attorney General Xavier Becerra has already issued a statement that he will seek to challenge the rule.