(Reuters) - Senate Banking Committee Democrats on Monday asked the panel’s Republican chairman in a letter to “clear the backlog” of 16 nominations by President Barack Obama to posts related to financial oversight, national security and other areas. The committee, led by Republican Senator Richard Shelby, has “failed to carry out one of its basic duties” for more than a year, the 10 Democratic banking committee senators wrote in the Feb. 22 letter. It is the only Senate committee that did not act on any nominees last year, the Democrats wrote. Of the 16 nominations pending before the committee, four have been waiting for action for more than a year while others have been “in limbo” for more than nine months, the Democratic senators wrote. Shelby must “stop obstructing” the nominations, they wrote in a separate statement. All 10 Democrats on the committee signed the letter, including Senators Sherrod Brown of Ohio, Elizabeth Warren of Massachusetts, and Charles Schumer of New York.  A spokeswoman for Shelby did not immediately respond to a request for comment. Shelby has said he is concerned that Obama has not nominated anyone as the U.S. Federal Reserve’s vice chair for supervision, a post created by the Dodd Frank financial reform law, but which has never been filled. “We are aware of your concern that the Administration has not nominated anyone to serve as Vice Chair for Supervision at the Federal Reserve, but the response to one vacancy should not be the creation of 16 more,” the Democratic banking committee senators wrote. It was unclear why President Obama has not appointed a nominee for the Fed post. A White House spokesperson was not immediately available for comment. The Senate Banking Committee backlog includes Lisa Fairfax and Hester Peirce, Obama’s two nominees to the Securities and Exchange Commission and Adam Szubin, nominated as the Treasury Department’s under secretary for terrorism and financial crimes. 