They don't call it the #BankLobbyistAct for nothing.

Big bank lobbyists have worked tirelessly to shape the massive deregulatory bill currently making its way through the Senate, and on Monday 13 financial institutions delivered what Sen. Elizabeth Warren (D-Mass.) derided as a "sweet thank-you note" to the Democrats and Republicans whose support has the measure's passage all but certain.

"Instead of seeking out thank you letters from big banks and their lobbyists, we should be working on what our constituents want. That's sure as heck not deregulating big banks."

—Sen. Elizabeth Warren

Signed by American Express, KeyCorp, SunTrust, and ten other banks, the letter expresses "appreciation and support for S. 2155, the Economic Growth, Regulatory Relief, and Consumer Protection Act," which is scheduled for a procedural vote on Tuesday.

"Bipartisan cooperation and compromise has led to the creation of legislation that would make sensible and incremental changes to existing regulation, support the extension of credit, and spur economic activity across America," the letter reads. "We encourage the Senate to act expeditiously to pass this bill."

Warren was quick to note on Twitter that the banks behind the jubilant thank-you note "got $30 billion in bailouts just a few years ago, but they are still able to get senators of both parties to do their bidding and roll back the rules."