Just a week after an emotional debate over government surveillance drove Congress to the edge, Democratic anger is again quickly mounting against Mitch McConnell.

Senate Democratic leadership wrote to the majority leader on Wednesday to urge him to back down from his "ridiculous" plan to attach cybersecurity legislation to an annual defense policy bill.

The letter, signed by Minority Leader Harry Reid, Minority Whip Dick Durbin, and Sens. Chuck Schumer and Patty Murray, asks McConnell to not tack the Cybersecurity Information Sharing Act on as an amendment to the National Defense Authorization Act, which is generally viewed as "must-pass" legislation.

"Adding CISA to the National Defense Authorization Act (NDAA) in a manner that allows neither debate nor amendment is ridiculous," the Democratic leaders wrote. "This is especially true given the President's commitment to veto the NDAA for unrelated reasons. This is a pure political ploy that does nothing to advance America's national security. We urge you to reconsider your efforts to jam through this important legislation in a manner that renders it meaningless."

McConnell on Tuesday announced that he would add CISA—which passed the Senate Intelligence Committee in March on a 14-1 vote—as an amendment to NDAA, noting the recent hack of the Office of Personnel Management that exposed the personal information of some four million current and former federal employees.

But that tactic has put McConnell under siege from Democrats, some of whom are generally supportive of the cybersecurity legislation but question the merits and motives of the majority leader's process.

CISA seeks to cajole companies into increasing their sharing of "cyberthreat" data with the government by offering them expanded liability protections, an arrangement the bill's backers say could help mitigate and potentially prevent devastating cyberattacks. Two similar versions of the bill easily passed the House last month with bipartisan support.

Privacy advocates warn that expanded public-private information sharing could enhance the government's surveillance capabilities, particularly at the National Security Agency, which will be able to access the data in or near "real time" as it migrates into government servers. Democratic Sens. Patrick Leahy, Ron Wyden, and Al Franken have said they have profound reservations about the privacy implications of the measure and have attacked McConnell for what they say is an attempt to limit debate.

But even some of the bill's supporters are lining up to excoriate McConnell's strategy. Earlier Wednesday, Sen. Dianne Feinstein, the top Democrat on the Senate Intelligence Committee who for years has pushed for information-sharing legislation, accused McConnell of trying to stifle debate, noting that lawmakers on both sides of the issue "want an opportunity to offer relevant amendments."

"A number of my colleagues would like to propose amendments, as is their right," Feinstein said on the Senate floor. "And I expect I would support some of them and would oppose some of them. But the Senate should have an opportunity to fully consider the bill, to receive the input of other committees with jurisdiction in this area."

Feinstein also suggested that McConnell's move could imperil bipartisan support for CISA.

A McConnell aide dismissed the notion that considering CISA as an amendment was stifling debate.

"Actually, there is plenty of time for debate. They can go debate now instead of a quorum call. And they can amend, we did not fill the tree," said McConnell spokesman Don Stewart in an email. "And let's not forget that when Sen. Reid was majority leader, he DID fill the tree on cyber, blocking ALL amendments."

Senate Intelligence Chairman Richard Burr filed CISA as a second-degree amendment to another amendment late Tuesday, a maneuver that means it will not be open to further changes during debate.