The new rule penalizes anyone who qualifies for assistance, even if that person doesn't use it.
Immigration authorities will assess whether an immigrant might qualify for public assistance programs in the future. The administration has expanded the definition of those public benefit programs to include Medicaid and food stamps.
Officials with U.S. Citizenship and Immigration Services evaluate applicants based on a "totality of circumstances," weighing factors like age, health and employment history.
Certain public benefits are exempt from the review process. If an applicant has needed emergency medical assistance, disaster relief or was enrolled in a discounted school lunch program, it will not count against them.
To whom does the rule apply?
Otherwise, the rule applies to people looking to come into the U.S. legally, as well as people who have already entered the country legally but are applying to become permanent residents.
The government says that on average 544,000 people seek green cards each year, and of that amount, about 382,000 are probably going to have to fill out a new special form, called a "declaration of self-sufficiency."
People who are in the country legally will be affected too.
The announced change rattled immigrant communities and could impact U.S. citizen children if parents decide not to use public services out of fear their green card application will be denied.
Researchers at the University of California San Diego found immigrants are less likely to seek out necessary medical care after being told about the public charge rule.
With the addition of food stamps as a disqualifying factor on applications, advocates worry about disadvantaged immigrants not having access to basic food.
While people in the country illegally cannot enroll in government programs like food stamps, many families with U.S. citizen children could qualify.
The data on how many people opted not to access benefits because of fear of their immigration status is limited. But a nonpartisan policy group Children's HealthWatch found last fall that SNAP enrollment was already down 10% among immigrant families last year.
Experts say the change complicates and strains an already overburdened immigration process.
Green card applicants will be faced with new paperwork and additional legal hurdles to prove they won't need U.S. public services. USCIS officials reviewing applications will also require additional training to calculate those positive and negative traits.
"It's going to really slow things down," said Jeffrey Gorsky, a senior immigration attorney at Berry Appleman & Leiden and former chief legal adviser for visas at the U.S. State Department.
Referencing the Trump administration's attempt to institute a similar policy through the state department, Gorsky said the latest move is another attempt to block immigrants without closing the border.
"They've slowed things down and I think that's been deliberate," he said.
The Trump administration will face legal challenges -- again.
Officials in California are expected to sue the administration over the rule shift, saying it wrongfully disqualifies immigrants who meet the legal requirements for citizenship.
"This vile rule is the Trump Administration's latest attack on families and lower income communities of color," California Attorney General Xavier Becerra said in a statement. "We will not stand idly by while this Administration targets programs that children and families across our state rely upon."
Congressional Democrats have introduced legislation to block funding to the Department of Homeland Security over the new rule.
Multiple advocacy groups have also promised to take the administration to court, citing both the impact on immigrant communities and what they call a rushed process for implementing the regulation.
"This policy denies a permanent, secure future in this country to anyone who isn't white and wealthy," said Marielena Hincapié, executive director of the National Immigration Law Center.
Much of the administration's immigration agenda has ended up in court. For example, lawsuits have stalled progress on Trump's border wall and created hurdles for the new policy to make asylum seekers wait in Mexico.
ABC News' Stephanie Ebbs and Sophie Tatum contributed to this report.