A gentlemen’s agreement that Senate Democratic and Republican leaders made earlier this year to try to increase the chamber’s legislative output appears to be fraying in the wake of last week’s move by Democrats to remove an option to offer amendments.

The agreement “could potentially be out the window,” Sarah Binder, a historian of Congress at George Washington University and a senior fellow at the Brookings Institution, said Tuesday.

“It takes two to tango,” a Senate Democratic aide said.

At the beginning of the 112th Congress, Senate Majority Leader Harry Reid (D-Nev.) agreed not to “fill the tree” — a procedural move to prevent amendments from being offered to a bill — and Senate Minority Leader Mitch McConnell (R-Ky.) promised not to force Democrats to routinely file cloture on noncontroversial legislation.

But that agreement between the two leaders got its biggest test last week as Reid and McConnell squared off over legislation designed to blunt the effects of Chinese currency manipulation on the U.S. economy.

Democrats used a simple majority vote to prevent the minority from offering motions to suspend the rules after the Senate voted to cut off debate.

Before the change, motions to suspend the rules — which require 67 votes to pass and seldom succeed — were permitted after cloture was invoked.

The move came after Reid filled the tree on the currency legislation, following an effort by McConnell to force a vote on President Barack Obama’s jobs bill.

Democrats took the step, according to the Senate Democratic aide, because Republicans had threatened to force nine motions to suspend the rules for votes on amendments to the currency bill.

“You can’t reach an agreement with people who negotiate in bad faith,” the aide said.

In a Washington Post op-ed Tuesday, Reid said that Democrats’ actions last week would restore order in the Senate.

“The Senate’s rules honor the rights of the minority party, and the right of every individual senator, to influence and shape the debate. That right of an individual senator to stand up and speak until the body votes to stop that debate, is balanced by a tradition of cooperation and conciliation. The Senate moves by consent.

“But in recent years, the minority party has abused its right to debate and delay, and has upset the balance between minority rights and cooperation on which a productive Senate depends,” Reid wrote.

A Senate GOP aide said the term obstructionist doesn’t apply to the Republicans because “just since returning from August recess, the Senate passed, in a bipartisan way, the patent reform bill, Trade Adjustment Assistance, a highway bill extension and the [Federal Aviation Administration] extension — all have been signed into law by the president; all have been called job-creators by Sen. Reid. And on Wednesday, we’ll pass three free-trade agreements, which Republicans and the president, in a bipartisan way, agree are significant job creators.”

The GOP aide also said that the motions to suspend the rules have not been abused and none have been brought up this year.

At issue for the Republicans is that they lost one way to affect legislation in the minority.

“Not only does [Reid] have the ability to fill the tree, but he now has the ability to prevent motions to suspend the rules after cloture,” the Republican aide said.

Democrats contend their action had nothing to do with any particular amendment but with the ability to move legislation through the Senate.

“This [motion to suspend the rules] is a new stalling tactic,” the Democratic aide said, arguing that the threat for filibuster by amendment was afoot and that the move had been used about 18 times last year.

“Our problem was with running through a gauntlet of potentially unlimited amendments on a bill that had broad bipartisan support, not about any amendment,” the aide continued.

Binder said she doesn’t think the Democrats’ move is a momentous precedent. She said she believes the move is an effort to make sure that invoking cloture puts the Senate on a path to a final vote.

“From my perspective, ever since they lowered the threshold for cloture in 1975, there have been efforts to make sure that cloture actually does bring the Senate to a final vote,” Binder said. “This really is another move in that direction.”

But from the minority’s point of view, Binder said, “it’s clamping down on an avenue” to affect legislation.