WASHINGTON -- Sen. Richard Shelby, R-Tuscaloosa, is blocking Senate action on executive branch nominations, a spokeswoman for Senate Majority Leader Harry Reid, D-Nev., said this afternoon in an e-mail.

In response to a question from the Press-Register, Reid spokeswoman Regan Lachapelle confirmed that Shelby has placed a "blanket hold" on most pending nominations.

By placing a hold, a single senator can stop the Senate from voting on a particular nomination, often as a way of gaining leverage on an unrelated issue. It is not clear when Shelby placed the hold or how many nominees are affected. While individual holds are not unusual, Gary Jacobson, a congressional expert at the University of California at San Diego, said he knew of no previous use of a blanket hold.

Shelby spokesman Jonathan Graffeo did not immediately respond to phone and e-mail messages seeking confirmation of the senator's action or his reason for doing so.

Holds can be overcome, but it takes 60 votes in the 100-member Senate. While tradition-bound senators are typically reluctant to take that step, they did so Thursday in voting to confirm nominees to the Labor Department and the General Services Administration.

(For a complete report, see Friday's Press-Register.)

(Updated at 2:50 p.m. with Jacobson comment and at 3:05 with update on Senate action.)