US President Donald Trump’s administration is to make it more difficult for poorer legal migrants to extend their visas or gain permanent resident status (a green card).
The rule targets migrants who rely on public assistance, such as food aid or public housing, for more than a year.
Their applications will be rejected if the government decides they are likely to rely on public assistance in future.
The rule change would reinforce “ideals of self-sufficiency,” officials said.
Immigrants who already hold a green card are unlikely to be affected.
The new regulation, known as a “public charge” rule, was published in the Federal Register on Monday and will take effect on 15 October.
Applicants who do not meet income standards or who are likely to rely on benefits such as Medicaid (government-run healthcare) in future will be blocked from entering the country.
Those already in the US would not be able to obtain green cards or US citizenship.
President Trump has made immigration a central theme of his administration. Last week, about 680 people were arrested in the state of Mississippi on suspicion of being undocumented migrants.
Pictures emerged of children crying after being separated from their parents. Officials said they took steps to ensure any children were properly cared for.
The White House says two-thirds of immigrants entering the US “do so based on family ties rather than on skill or merit”.
More than three-quarters (78%) of households headed by a non-citizen with no more than a secondary school education used at least one welfare programme, it said.
The number of would-be migrants apprehended at the US southern border with Mexico has been rising over the last two years.
However, the number of undocumented immigrants in the US is falling, according to recent analysis from the Pew Research Center.
In May, President Trump put forward proposals for a new skills-based immigration system, designed to favour younger, better educated, English-speaking workers.