The Senate could be stuck in town through Sunday or even later, Democratic leaders warned their members on Thursday.

Republican objections are keeping Senate Democrats from moving to a House-passed Medicare bill, and could keep the upper chamber in session if the impasse continues.

“Senators should be prepared to adjust their schedule so they can be here for the Sunday vote and any other votes,” reads an e-mail sent to Democratic senators and aides.

“As a result of these objections, we will not be able to move to proceed to the bill and file a cloture motion on the motion to proceed until after midnight tonight. That would mean the cloture vote on the motion to proceed would not occur until Sunday, June 29th,” the e-mail said.

Although the Senate has other pending business, such as war funding, a housing bill and legislation to authorize wiretapping, a spokesman for Majority Leader Harry Reid (D-Nev.) emphasized that the Medicare bill has a firm deadline. “Medicare definitely needs to happen,” the spokesman said, while some other business could wait until the Senate returns from its scheduled recess next week.

Unless Congress acts, physicians will see their Medicare fees reduced by 10.6 percent on July 1, which is next Tuesday. Lawmakers want to go home but are not eager to face angry physicians when they get there, as well as pharmacists, wheelchair vendors and other business owners who would benefit from the Medicare bill.

The House passed the measure Tuesday in an overwhelming 355-59 vote. Senate Democrats, noting the veto-proof majority, quickly dropped out of delicate bipartisan negotiations that had been under way and lined up behind the House-passed bill.

Most House Republicans, though excluded from drafting the bill, voted for it anyway to avoid blowback at home, and GOP senators may make the same calculation rather than cut into their vacation.

A Senate bill similar to the House-passed measure failed to obtain cloture on a 54-39 vote June 12. That tally, however, did not include the votes of seven senators who were not present. If presidential candidate Sen. Barack Obama (D-Ill.) and the rest of the absent senators, with the exception of ailing Sen. Edward Kennedy (D-Mass.), attend and support the House-passed bill, Democrats would need just one more Republican to come aboard.

The White House, however, has threatened to veto the measure, mainly because it would cover the cost of fixing physicians’ pay by taking money from the private health insurance plans in the Medicare Advantage program. Many congressional Republicans also object to those cuts.