U.S President Donald Trump’s administration unveiled a new rule on Monday that could deny permanent residency to hundreds of thousands of people for being too poor.

The long-anticipated rule, pushed by Trump’s leading anti-immigration aide Stephen Miller, takes effect in mid-October and would reject applicants for temporary or permanent visas for failing to meet income standards or for receiving public assistance such as welfare, food stamps, public housing or Medicaid.

Such a change would ensure that immigrants “are self-sufficient,” in that they “do not depend on public resources to meet their needs, but rather rely on their own capabilities, as well as the resources of family members, sponsors, and private organizations,” a notice published in the federal register said.

This could be the most drastic of all the Trump administration’s anti-immigration policies, experts have said. Advocates for immigrants have criticized the plan as an effort to cut legal immigration without going through Congress to change U.S. law.

Under the new rules, more than half of all family-based green card applicants would be denied, according to the migration policy institute, a research organization. Some 800,000 green cards were granted in 2016.