Sen. Mel Martinez, is resigning, a senior Republican official told FOX News.
The first-term senator, who announced last year that he wouldn't seek re-election in 2010, told his staffers at a meeting Friday morning that will not return to the Senate after the August recess.
"My priorities have always been my faith, my family and my country and at this stage in my life, and after nearly 12 years of public service in Florida and Washington, it's time I return to Florida and my family," Martinez said in a letter to friends and supporters, obtained by FOX News.
"So today I'm announcing my decision to step down from public office, effective on a successor taking office to fill out the remainder of my term."
Martinez, the only Hispanic Republican in the Senate, will make a formal announcement at a news conference planned for Friday at 3 p.m. in Orlando.
The news immediately drew attacks from Democrats.
"Republicans seem to have a problem fulfilling their oaths of office," said Democratic Senatorial Campaign Committee spokesman Eric Schultz said in a written statement. "This is the largest number of retirements for one party in the Senate in the past 80 years."
"The country faces enormous challenges right now, and voters are watching who is up to the task," he added.
Several sources told FOX News that Martinez wants to return to Florida to help resolve some family issues.
Rumors had been swirling for months that Martinez would resign early.
His resignation will allow Gov. Charlie Crist, who is running for the seat, to appoint a replacement. Sources told FOX News that Crist will appoint a placeholder and let the primary unfold as usual. But Crist is not likely to appoint himself because it could alienate voters.
It is unclear whether Martinez would endorse a candidate.
With Democrats holding a commanding 60-seat majority in the Senate, every seat is critical for Republicans. The Florida race has captured national attention because it is one of several contests in which the GOP must find strong candidates to run.
Martinez announced in December that he would not seek a second term in 2010, also citing a desire to spend more time with his family.
He denied that he faced difficult re-election prospects in a state won by President Obama. But he has struggled to boost public support because of his close ties to President George W. Bush and his efforts pushing an immigration bill that was unpopular with many Republicans.
Martinez was elected in 2004 after serving as the U.S. secretary of housing and urban development during the Bush administration. He served as general chairman of the Republican National Committee for 10 months, resigning in October 2007.
