Senate Democrats and Republicans have reached an agreement over constraints to the Federal Reserve’s emergency lending powers, clearing a last remaining hurdle for a $900 billion pandemic aid package. The compromise wouldn’t prevent the central bank from creating similar programs in the future, according to aides from both parties.

A Republican push to curtail the Federal Reserve’s emergency lending powers kept congressional leaders from completing a $900 billion coronavirus relief package for a second day Saturday, as lawmakers scrambled to compromise on the late-emerging dispute.

Congressional leaders agreed to the contours of the sweeping relief package earlier this week and have said for days that they were close to finalizing its details. The last-minute fight over the Fed provision from Sen. Pat Toomey (R., Pa.) remained an obstacle Saturday evening, as lawmakers worked to see if they could find a compromise.

Senate Democrats and Republicans have reached an agreement over constraints to the Federal Reserve’s emergency lending powers, clearing a last remaining hurdle for a $900 billion pandemic aid package. The compromise wouldn’t prevent the central bank from creating similar programs in the future, according to aides from both parties.

A Republican push to curtail the Federal Reserve’s emergency lending powers kept congressional leaders from completing a $900 billion coronavirus relief package for a second day Saturday, as lawmakers scrambled to compromise on the late-emerging dispute.

Congressional leaders agreed to the contours of the sweeping relief package earlier this week and have said for days that they were close to finalizing its details. The last-minute fight over the Fed provision from Sen. Pat Toomey (R., Pa.) remained an obstacle Saturday evening, as lawmakers worked to see if they could find a compromise.

“They have achieved their purpose. They should come to an end, they should not be restarted and a replica should not be created. That’s all,” Mr. Toomey said on the Senate floor Saturday.

Sen. Bill Cassidy (R., La.) said he thought a deal could emerge with “a more narrow focus” on the Fed provision.

Currently, the Fed and the Treasury Department are allowed to establish any emergency-lending programs if they agree jointly. In deciding to end the current lending programs, Mr. Mnuchin had said the Fed and Treasury would be free to restart them next year with a different funding source.

Fed Chairman Jerome Powell has made the same point, including at a news conference on Wednesday, in an effort to reassure markets should conditions deteriorate.

While some Democrats are willing to rescind the funding associated with these programs and end them on Dec. 31, they have drawn a line at measures that would prevent the Fed and the Treasury Department from starting new programs next year if they see the need.

“This is not a time to take away long-existing authority from the Fed to deal with this crisis,” Sen. Elizabeth Warren (D., Mass.) said.

Not all Republicans agreed with Mr. Toomey’s push.

“My view is the Fed’s capacities should be returned to the condition they were in prior to the Cares Act, but if we’re going to have major reforms to the Fed, this is not the time for that,” Sen. Mitt Romney (R., Utah) said Saturday.

Others said they were backing Mr. Toomey and were willing to delay reaching a final agreement. Mr. Mnuchin indicated on Saturday’s call with Senate Republicans that he supported Mr. Toomey’s proposal, according to people familiar with the discussion.

Senate Majority Whip John Thune (R., S.D.) said work had continued on crafting the legislative language for the less-controversial parts of the bill to speed the process up once a deal is completed, but said it was possible the process would spill into Monday or later.

The White House has pushed for a resolution, and Mr. Trump has been particularly eager to secure another round of direct-assistance checks to households, GOP lawmakers said. The disagreement could bump Congress into its next spending deadline. On Friday night both chambers passed a two-day spending patch, signed into law by President Trump, to keep the government funded through Sunday while negotiations continued.

The president has “made clear he wants the next round of relief to include stimulus checks at a significant number. We’re working with Congress to settle on an agreement that can pass as soon as possible,” White House spokesman Ben Williamson said on Friday.

Lawmakers were also working out differences Saturday surrounding the distribution and eligibility requirements of the roughly $600 direct checks expected to be included in the final bill, the duration and limits around a temporary increase in food-stamp benefits, and how to structure a relief program for live-performance venues and other industries seeking aid.