Treasury Secretary Janet Yellen, in a letter on Friday to congressional leaders, said the Treasury would begin using extraordinary measures Jan. 21.

In one of her last acts as U.S. Treasury Secretary, Janet Yellen said her agency will start taking “extraordinary measures,” or special accounting maneuvers intended to prevent the nation from hitting the debt ceiling,

A key deadline for the government's borrowing limit is rapidly approaching, but lawmakers may not have to deal with it until the summertime.