Senator Mel Martinez (R-Fla.) is resigning, possibly making the announcement as early as Friday, according to NBC news.
Whether announced Friday or not, sources say the resignation will be official at some point in August, with the hope of having a replacement in office when the Senate comes back from its recess.
Martinez made the announcement at a morning staff meeting, where he said he will not be returning to the Senate after the August recess.
Martinez had already planned to retire at the end of 2010. Florida Governor Charlie Crist (R) has announced that he will run for Martinez's seat. The resignation will not change the balance of power in the Senate as Crist would likely appoint a Republican to fill the vacancy.