Talks on border security funding collapsed after Democratic and Republican lawmakers clashed over immigrant detention policy as they worked to avert another U.S. government shutdown, a Republican senator said on Sunday.

“The talks are stalled right now,” Republican Senator Richard Shelby told “Fox News Sunday.” He said the impasse was over Democrats’ desire to cap the number of beds in detention facilities for people who enter the country illegally.

Efforts to resolve the dispute over border security funding extended into the weekend as a special congressional negotiating panel aimed to reach a deal by Monday, lawmakers and aides said.

Democratic Senator Jon Tester played down any breakdown in talks. “It is a negotiation. Negotiations seldom go smooth all the way through,” he told the Fox program. Tester, one of 17 negotiators, said he was hopeful a deal could be reached.

But Shelby put the chances of reaching a deal by Monday at 50-50. No further talks were scheduled, a source told Reuters on condition of anonymity.

The lawmakers hoped to have an agreement by Monday to allow time for the legislation to pass the U.S. House of Representatives and Senate and get signed by President Donald Trump by Friday, when funding for the Department of Homeland Security and other federal agencies expires.