“This effort to turn back the clock on civil rights is coming at a most inopportune time, and the Trump administration is keenly aware of it,” Lisa Rice, the president of the National Fair Housing Alliance, said in a call with reporters.

Civil rights groups fear that the Trump administration’s new rule will make it far harder to challenge housing discrimination. Sherrilyn Ifill, the president and director counsel of the NAACP Legal Defense and Educational Fund, called the five-part requirement “an incredible and extraordinary burden” that makes it “virtually impossible to prevail.” On top of that, she said in a call with reporters, the defenses made available to the defendants are “astonishing.”

But stopping the change will be difficult. Congress has 15 days to review the proposal. Once it has been published on the Federal Register, there will be a 60-day comment period. And the HUD rule might set the standard for much of the federal government. Similar action is under consideration at the Education and Justice Departments.

The proposed change dates to last summer, when Anna Maria Farías, HUD’s assistant secretary for fair housing and equal opportunity, announced that she would be amending the standards for discrimination that the Obama administration adopted in 2013. Ms. Farias cited a Supreme Court decision in 2015 on discrimination claims in fair housing.

The new rule, which has yet to be published in the Federal Register, would force those initiating lawsuits not only to show that a specific housing policy has a discriminatory effect, but also to show that the effect is “arbitrary, artificial and unnecessary” in achieving a “legitimate objective.” There must also be a “robust causal link” between the specific policy and the discriminatory effect.