With the first cluster of appropriations bills due on the Senate floor next week, Republicans must decide whether to fight now or later over spending and policy priorities.

If the GOP opts to band together and vote against the three-bill “minibus” Senate Appropriations Chairwoman Barbara A. Mikulski plans to bring to the floor, it would effectively put an end to what’s widely been viewed as Congress’ best chance in years to pass and conference spending bills ahead of the Oct. 1 start of the fiscal year.

The Maryland Democrat said last week that she plans to bring forward a package of spending bills that contains the Commerce-Justice-Science (S 2437), Transportation-HUD (S 2438) and Agriculture (S 2389) measures. All have emerged from Senate Appropriations in recent weeks with broad bipartisan support.

Even though most of the committee’s Republicans backed the measures, they said they disapprove of how Democrats divided more than $1 trillion in fiscal 2015 discretionary dollars between the 12 appropriations bills. They also said the allocations rely too heavily on budgetary “gimmicks” in order to meet the budget caps codified as part of the December budget deal (PL 113-67).

Sen. Richard C. Shelby of Alabama, the committee’s ranking Republican, has vowed to work to change the top line figures either on the Senate floor or later in the appropriations process.

Republican concerns over allocations “have to be addressed, sooner rather than later: on the floor, in conference, one way or the other,” he said recently.

Mikulski has vehemently defended her 12 top-line allocations, saying she “did not invent new tools” and that her top lines are “faithful to both the spirit of the [budget] agreement and the law itself.”

Amendment Concerns

But allocations are only one issue facing the spending bills.

Many Republican senators say they would be willing to consider the spending bills — even with the allocations they don’t like — if Democrats don’t limit floor amendments.

“We’d like a process that at least allows us to get votes on amendments,” said John Thune of South Dakota, a member of the GOP leadership team.

“As long as members are allowed to bring amendments as long as they want to, I’m certainly prepared to defend the [agriculture] portions of the bill,” said Roy Blunt of Missouri, ranking Republican on the Agriculture Appropriations subcommittee.

They said they don’t expect Senate Majority Leader Harry Reid would allow such open consideration; the Nevada Democrat has tended to control the amendment process quite tightly in recent years.

Mikulski said “relevant amendments” to the Agriculture, C-J-S and Transportation-HUD spending bills would be allowed on the floor, but she said Reid is still sorting out whether an unlimited number of such amendments would be an option.

“What we want is amendments germane to the bill,” Mikulski said Thursday. “So the bills that we’re moving next week are not foreign policy bills, they’re bread-and-butter bills.”

While it is still unclear which kinds of amendments would be considered “germane,” the fact that Democrats are opening the door for Republican input is still a critical distinction that could significantly up the chances for passage.

The three upcoming spending measures “are three bills that members are generally going to be favorably disposed toward, and if you combine that with a process that let’s individual members challenge what’s in the bill, it reminds the Senate of why we’re for what for,” said Blunt. “I’m anxious see this process begin to work.”

Labor-HHS-Education Stalls

Even as the first bills move to the Senate floor, there are signs that a delay in moving one spending measure out of committee could reflect ongoing Democratic concerns over amendments.

Earlier this week, the Appropriations Committee put a planned — but not formally announced — markup of the contentious Labor-HHS-Education on hold and said it is “under review” without any explanation.

Sen. Tom Harkin, D-Iowa, chairman of the subcommittee that oversees the $156.8 billion spending bill, and Republican appropriators have hinted that the markup was killed by Democratic leadership to shield politically vulnerable Democrats on the panel, such Mary L. Landrieu of Louisiana and Mark Pryor of Arkansas, from taking votes related to the health care law.

Dan Coats of Indiana, a top GOP appropriator, said one could potentially read the action as a sign the chamber’s Democrats do not want to take tough votes on spending bills, especially on the floor.

“The reason the Appropriations Committee canceled their markup was their members didn’t want to take any hard votes. They know they’re vulnerable this year, in this election,” Coats said.

On the pending package, the C-J-S bill could particularly attract amendments on politically-charged issues like gun control, the transfer of detainees held in Guantánamo Bay, Cuba, and medical marijuana that Democrats may want to shy away from.

Some senior Democratic appropriators said they’re ready for any challenges floor consideration may bring.

“It’s been so darn long since we’ve started up this bus. There’s a real question as to how it will work and whether we can get it through the floor in an efficient way,” said Richard J. Durbin of Illinois, chairman of the Defense Appropriations subcommittee and the Senate majority whip. “But we’ve got to start somewhere. I think these three bills are good places to start.”

Niels Lesniewski and Humberto Sanchez contributed to this report.