WASHINGTON — The Senate inched Friday toward a final vote on a major government funding bill to keep a slew of agencies afloat through September. But the timing of a final vote remains up in the air, with the possibility of a brief shutdown lingering.

A procedural vote Friday passed 63-35 in the afternoon, triggering up to 30 hours of debate. But speeding that up requires all 100 senators to agree, and numerous Republicans have demanded votes on amendments, including immigration-related measures seen as poison pills. Talks continued ahead of a midnight deadline, with aides uncertain that they could finish before a partial government shutdown takes effect on Saturday.

“It’s gotten a little complicated, unfortunately,” said Senate Minority Whip John Thune, R-S.D. “Hopefully we can avoid [a shutdown] but that’s going to involve the Democrats being willing to work with us on some amendment votes.”

Senate leaders face a tricky balance: If an amendment comes up and passes, it would disrupt the deal and send the bill back to the House, which would all but guarantee a shutdown.

“We have until tonight for the Senate to send an appropriations package to the president, or else the government will begin to shut down,” Senate Majority Leader Chuck Schumer, D-N.Y., said Friday. “I hope my Republican colleagues will work with us on a reasonable agreement so we can get this funding package done today and send it to the president’s desk before a shutdown.”

A partial government shutdown would affect the Departments of Justice, Commerce, Agriculture, Transportation and many other parts of the government. But it is expected to last less than 24 hours with limited impact during the weekend if senators miss the midnight deadline. The Senate has the vote to pass the funding bills, but members seeking amendment votes can delay passage until Saturday evening.

The 1,050-page measure is a package of six appropriations bills negotiated by Schumer, House Speaker Mike Johnson, R-La., President Joe Biden and top appropriators in both parties and chambers.

The package passed the House on Wednesday by a vote of 339-85. After Senate passage, which is all but assured whenever the vote occurs, it will go to Biden’s desk to be signed into law.

Sen. Susan Collins, R-Maine, the appropriations vice chair, warned that there will be “a partial government shutdown” if the bill doesn’t pass by midnight.

“Do we really want a veteran who has bravely and loyally served his country, and is now trying to file a claim for benefits, to find that the Veterans Benefits Administration’s doors are closed to him or her?” she asked. “Is that what we want to have happen?”

Next funding deadline: March 22

Tougher work still lies ahead. The remaining six appropriations bills, which include contentious issues like how to fund the Department of Homeland Security, face a deadline in just two weeks, on March 22. Negotiators haven’t reached a deal on that yet.

Rep. Rosa DeLauro, D-Conn., the top Democratic appropriators in the House, said the remaining six bills are “in various stages of negotiations” as “staff on both sides of the aisle, in both chambers, are working on them.”

“We worked hard to get these done,” DeLauro said. “I’m optimistic about getting the next six done.”

Schumer has praised both parties’ work on the initial six bills.

“The process never is easy in divided government, but with hard work, cooperation, and persistence, good things can happen if we put working together before other extraneous and often destructive issues,” Schumer said, adding that it is “noteworthy that a majority of both parties in the House, a majority of even the Republicans, supported this legislation.”

Johnson, for his part, said the bill contains conservative wins including cuts to the FBI, Environmental Protection Agency and Bureau of Alcohol, Tobacco, Firearms and Explosives. He said Republicans achieved that “with divided government and a historically small House majority.”

Democrats have highlighted the package’s funding for WIC, food assistance for women, infants and children, among other wins.

Biden hopes to sign it into law before a partial government shutdown occurs on Saturday morning at 12:01 a.m. ET.