They have the power to do it and are threatening to use that power if Democrats even try to "tweak" the filibuster rules, according to Brad Plumer at WaPo's WonkBlog.
The GOP could find other ways to bog down legislation beyond the filibuster. Or the party could go nuclear and prevent the Senate from getting any business done whatsoever. “It’s all a matter of degree and how much they wanted to ratchet up the response,” says Sarah Binder of George Washington University.More on taking steps to curtail use of the filibuster here.
For starters, as Jonathan Bernstein points out, there are all sorts of incremental steps Republicans could take to bog down Senate business if Democrats tweaked the filibuster rules. Right now, for example, the minority doesn’t usually demand its allotted 30 hours of post-cloture debate time. That could change. Of course, the problem here is that Democrats could threaten to change those rules with 51 votes, as well. So this might not be a convincing threat.Alternatively, the GOP could threaten to shut down the Senate entirely. This is technically doable. ...Plumer, WaPo