Washington — The Trump administration on Monday began enforcing stringent income-based requirements for green cards and certain visas, instituting the most ambitious unilateral effort in recent history to change the nation's legal immigration system.

After multiple legal barriers blocking the implementation of the new requirements were cleared by the conservative-leaning Supreme Court, most green card applicants in the U.S. and abroad will now be subjected to a redefined "public charge" test. Under the rules by the Departments of State and Homeland Security, immigration officials have more power to deny applications from petitioners they deem are, or could become, an economic burden on the country.

The sweeping policy change, one of the administration's top immigration priorities, is expected to block the entry of hundreds of thousands of people, disproportionately affecting prospective immigrants from Asia, Africa and Latin America, according to experts.

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Since it unveiled the final regulation last summer, the administration has portrayed it as a way to promote "self-sufficiency" among immigrant communities. "(The rule) enforces longstanding law requiring aliens to be self-sufficient, reaffirming the American ideals of hard work, perseverance and determination," said Ken Cuccinelli, the acting deputy secretary of the Department of Homeland Security.

Immigrant advocates and Democrats, however, say the rule amounts to a wealth test that will revive a discriminatory immigration system that shuts America's doors to low-income and working-class immigrants from the developing world.

"In 1924, our policy explicitly made it much harder for people from some parts of the world than others to come here. There were country-based quotas and there were country-based categorical exclusions for Asian immigrants," Julia Gelatt, a senior analyst at the nonpartisan Migration Policy Institute, told CBS News.

"Today, it's not quite as explicit, but by placing such drawn emphasis on people's income and income potential, by putting in place what is essentially a wealth test, this public charge rule could have some of the same impact of reshaping our immigration system to be more European and less Latin American," Gelatt added.

Soon after its final version was published last summer, the rule was blocked in court, with one federal judge in New York calling it "repugnant to the American dream." However, circuit courts subsequently lifted three of the four nationwide injunctions. The administration then turned to the Supreme Court, which lifted the remaining nationwide injunction last month, as well as a state-wide injunction in Illinois on Friday, allowing officials to enforce the policy on Monday across the country.

In a withering dissenting opinion on Friday, Justice Sonia Sotomayor expressed concern about the conservative majority's recent decisions allowing the Trump administration to move forward with fundamental policy changes without cases being decided on merit.

"Perhaps most troublingly, the Court's recent behavior on stay applications has benefited one litigant over all others," Sotomayor wrote in her opinion, noting the conservative jurists on the bench have repeatedly sided with the administration.

A "broad and sweeping" definition of public charge

For decades, the U.S. has asked most green card and visa petitioners to prove they won't be a "public charge" — or an economic burden — on the country.

The term dates back to a time period in U.S. history when the government actively sought to severely limit immigration from developing, non-white countries. It was first codified in U.S. law in 1882, the same year the U.S. enacted the discriminatory Chinese Exclusion Act, which barred the entry of most Chinese immigrants on the premise that they jeopardized "the good order of certain localities."

In the late 1990s, the Clinton administration issued guidance saying only cash benefits could be considered when determining whether an immigrant could be a "public charge." The Trump administration's policy, however, substantially expands this centuries-old term by broadening the type and amount of benefits — as well as income-based factors — that count against immigrants seeking to stay or move to the U.S.

"This certainly is a very broad and sweeping use of the public charge legislation," Gelatt said.

Under the new regulation, caseworkers would consider enrollment in the widely used Supplemental Nutrition Assistance Program (SNAP), certain federally funded Medicaid benefits and a variety of forms of government-subsidized housing, including the popular Section 8 vouchers.

Officials would deem an immigrant a "public charge" and deny the application if they determine he or she is more likely than not to use one of the considered benefits for 12 months or longer over the span of three years. On certain occasions, those deemed a "public charge" could post a bond for an amount no less than $8,100.

To determine whether prospective immigrants are likely to become a "public charge," caseworkers would also take into account their income, assets, age, educational skills, English language proficiency, health and other factors. Since those expected to be affected by the rule are not eligible for most public benefits because they are not U.S. citizens or permanent residents, critics of the regulation say it is designed to severely restrict immigration based on those factors.

Advocates have also denounced harmful effects the rule is having on people who are technically not directly affected by it but who are scared that the use of any public benefits might jeopardize their or their family's immigration cases. Researchers have been documenting a "chilling effect" stemming from the proposed changes that has prompted fearful immigrant families, some with U.S. citizen members, to drop out of essential welfare programs.

To curb this confusion and fear, advocacy groups and local officials have staged public awareness campaigns. Organizations like the Legal Aid Society, Make The Road New York and Empire Justice Center have created tools for lawyers and advocates to advise and screen immigrants on the new requirements.

"The implementation of the public charge rule today is a devastating blow for all Americans. The rule is heartless, cruel, and betrays our core values as a nation of immigrants," Kristin Brown, president of the Empire Justice Center, said in a statement. "This public charge screening tool will guide community-based organizations in helping families make crucial decisions that may carry life-changing consequences."