Could senators eliminate filibusters of executive branch nominees without affecting judges or legislation?

Procedurally, it might well be possible, but critics of the plan that Senate Majority Leader Harry Reid, D-Nev., appears ready to bring to his caucus Thursday afternoon are already raising that question.

Sen. Jeff Merkley, D-Ore., is among the leading supporters of modifying Senate rules to curtail the perceived abuse of unlimited debate rules, which effectively require 60 votes to cut off debate on much of the chamber’s business. Merkley has proposed far more expansive plans to change the rules than what he says Reid may bring forward.

“Certainly we’re doing the right thing now in preparing to have a major debate over the ability to have executive nominations,” Merkley said at a Center for American Progress Action Fund event Wednesday. He met with Reid on Tuesday to discuss the issue.

While what may be debated behind closed doors at a Thursday Democratic caucus lunch seems pretty narrow, it may be tough to unring the bell if a “nuclear option” is in fact deployed on the floor. Under such a procedural move, a simple majority would assert the ability to change rules and procedures without the two-thirds vote needed to overcome a filibuster of a formal rules changes.

Senate Armed Services Chairman Carl Levin of Michigan has been the most vocal opponent of the nuclear option on the Democratic side. He conceded it may be technically possible to make a narrow change in the rules applying to disputed executive branch nominees but said that, eventually, the dam would break to kill all filibusters.

“Maybe they could figure out a way that this time, this is what we’re doing, but that doesn’t mean that the same approach couldn’t be used for something else at a later time,” Levin said.

Following a Tuesday House vote on funding the Yucca Mountain nuclear repository in Nevada, Republican Sen. Dean Heller again referred to the project as a reason to avoid filibuster changes.

“Nevadans need no further reminder than tonight’s vote that members of the U.S. House of Representatives, regardless of party affiliation, seek to dump their nuclear waste in Nevada. It is important for the delegation to continue to work together and use any arrow in our quiver to stop the opening of Yucca Mountain, including the filibuster rules of the U.S. Senate,” Heller said in a statement.

Levin’s found himself speaking with some of the same language used by Republicans.

“Once you use a mechanism … which effectively breaks the rules or does [in fact] break the rules, then I don’t see any reason why it couldn’t be used for other things like getting bills passed which repeal Obamacare or getting a bill passed which starts — has a federal right to work law or which gets … something passed which repeals Roe v. Wade,” Levin said.

Levin’s reference to the landmark Supreme Court opinion guaranteeing abortion rights came just before several other Democratic senators held a news conference in opposition to a measure being debated by the Texas Legislature that would impose significant restrictions on abortions in that state.

At that news conference, Sen. Barbara Boxer, D-Calif., said she didn’t expect Reid to push through a procedural change that would go nearly as far as changing the rules for legislative business.

“I haven’t seen any proposal to be that far reaching. What I have heard is that we are looking at the stalled nominees of the president’s team that have been waiting in limbo for more than 200 days. That’s my understanding,” Boxer said.

Leadership aides have said including lifetime judicial appointments or legislation in a proposal to curb filibusters could be substantially more difficult.

Intentionally or not, Levin’s reference to the anti-union legislation seemed like a gentle prod of the labor movement, which has aggressively backed the use of the nuclear option to ensure a quorum at the National Labor Relations Board. Communications Workers of America President Larry Cohen has been on a media blitz supporting the NLRB confirmations in recent weeks and months, and AFL-CIO head Richard Trumka said his members are engaged in a “full-fledged campaign.”

“I’ve been personally meeting with senators, explaining to them how important the NLRB is, how the system is being abused, and it doesn’t take much [explanation] when you say the system is being abused,” Trumka said. “We’re meeting with [senators] regularly. We’re having people come in from their home states to meet with them here and meet with them back in their home states. Some are very, very quiet meetings; some are less quiet meetings.”

Appearing at the event with Merkley, Trumka expressed optimism that Democrats would stand together leaving the Thursday meeting in laying down the law.

“I think what you’re going to have is a unified caucus coming out of there saying you’ve proven to us that you won’t keep your word, you’ve broken it twice. You’ve proven to us that this isn’t about the capabilities or the qualifications of the president’s nominees,” Trumka said. “This is about obstructionism, and if you continue to obstruct, we will use the rules to force you not to be able to obstruct.”

Under the most likely scenario, Reid could file debate-limiting motions to break potential filibusters of a series of Obama nominees, including the contested NLRB picks.

Humberto Sanchez contributed to this report.