WASHINGTON (CNN) - Sen. Mel Martinez, R-Florida, will announce that he is resigning his seat, three GOP sources tell CNN.
The sources said that Martinez will officially announce his intention to step down on Friday. The Florida Republican, first elected in 2004, announced in December of last year that he would retire in 2010.
Florida law states that Gov. Charlie Crist may temporarily appoint someone to the vacant seat until the next general election. As of Friday morning, it was unclear what Crist would do. Crist announced in May he would not seek another term as governor, and instead would run for Martinez's seat.
Martinez is the only Hispanic Republican in the Senate. He joined eight other Republicans Thursday in voting to confirm Judge Sonia Sotomayor as the first Hispanic justice to serve on the U.S. Supreme Court.
Democrats currently hold a tenuous filibuster-proof majority in the Senate, with 60 votes. Martinez is one of six Republicans who have stated they would not seek re-election in 2010. But the Florida senator is the second Republican who has decided to leave before the curtain drops on the 111th Congress next fall.
Sen. Kay Bailey Hutchison, R-Texas, recently announced her intention to quit the Senate three years before her term expires in order to run for governor next year.
The five other Republicans who are retiring include: Missouri Sen. Kit Bond, Kansas Sen. Sam Brownback, New Hampshire Sen. Judd Gregg, Kentucky Sen. Jim Bunning and Ohio Sen. George Voinovich.
Two Democrats will not run in 2010, Illinois Sen. Roland Burris and Delaware Sen. Ted Kaufman. Republicans must defend 19 seats next year, while Democrats must protect 18.
Full statement from Martinez:
Because you're a friend, I wanted you to know first about the decision I will announce today to step down from public office.
Twelve years ago I offered myself as a candidate for public office in Florida out of a deep sense of appreciation for what America and the people of Florida did for me as a young immigrant to this country.
In 1997, Kitty and I decided it was time to give back and we entered the public arena, first as Mayor of Orange County, then as a Member of the President's cabinet and now as a United States Senator. Through those experiences I have gained the greatest respect for the people of Florida and have enjoyed serving their interests.
When I began my term as Senator, I promised I wouldn't simply warm a seat; I promised to take on the difficult issues and work to make a difference. Keeping that promise has meant pressing for help and assistance for families struggling to keep their homes, their jobs, and their confidence that our country is safe.
And on that note, I am especially grateful to the men and women of our military and their families whom I have had the distinct honor of representing in Washington and I thank them for their service to our country.
As a US Senator, I have also had a platform to speak against the oppression of the Cuban regime and my hope for a better future for the people of Cuba. I will continue that lifelong passion in the next phase of my life.
I will always be grateful to the people of Florida for bestowing on me the singular honor of representing them in the United States Senate.
My priorities have always been my faith, my family and my country and at this stage in my life, and after nearly twelve years of public service in Florida and Washington, it's time I return to Florida and my family.
So today I am announcing my decision to step down from public office, effective on a successor taking office to fill out the remainder of my term.
I have enjoyed my time in the Senate and have the utmost respect for my colleagues and the institution. I especially thank Republican Leader Mitch McConnell for his guidance and insight.
I look forward to continuing to be an active and constructive voice on issues vital to Florida and our nation, and being an active member of Florida's Republican Party.
Lastly, Kitty and I would like to thank you for all your support. You have been helpful in countless ways. As I begin this new chapter in my life, I look forward to seeing more of you and your family.
(Updated 1 p.m.)