A tea party caucus of U.S. senators convenes Thursday for the first time, but one of the movement's biggest stars doesn't plan to be there.

The meeting -- at least for now -- is not on Sen. Marco Rubio's schedule, said spokesman Alex Burgos, who pointed out that the freshman senator had yet to make up his mind about joining any caucus.

``He's proud of his relationship with the tea party movement,'' Burgos said. ``He shares with the movement a commitment to tackling debt, defending the free enterprise system and restoring our limited government tradition. It's the same case with other causes that have been brought to our attention, he hasn't made any decision one way or the other.''

Getting Rubio, who harnessed conservative fervor to secure a come-from-way behind win, would bolster the influence of the tea party caucus, which was started by Kentucky Sen. Rand Paul. He calls the caucus a ``direct reaction to the demands Americans made at the polls in November.'' Paul and two other founding members will meet with movement activists to discuss ``bringing an end to our nation's deficit, and limiting the size and scope of the federal government.''

The caucus members are Rand, Sen. Mike Lee, R-Utah and South Carolina Sen. Jim DeMint, who backed Rubio's fledgling Senate campaign even as the Republican party backed former Gov. Charlie Crist. They will meet in a Senate office building with leading tea party activists including Campaign for Liberty president John Tate, Americans for Tax Reform president Grover Norquist and Tea Party Express chairman Amy Kremer.

``The folks who made the tea party such a force to be reckoned with in the last election can have an enduring impact by holding elected officials accountable to the people,'' DeMint said in a statement announcing the caucus. ``They will be watching to see if those they helped elect make good on their limited government promises, and I intend to help them stay informed and engaged.''

The conservative caucus could pose a threat to the more moderate Senate Minority Leader Mitch McConnell, who has tangled with DeMint over federal spending on special projects. Some conservatives have taken notice that Rubio was among the freshmen senators invited to accompany McConnell last week on a high-profile trip to Pakistan and Afghanistan, where dined with Afghan President Hamid Karzai and met with Gen. David Petraeus, the U.S. top commander in Afghanistan.

Kremer, who said the tea party movement is aimed at ``sending conservatives to Washington, not Republicans,'' acknowledged a ``little bit of disappointment'' that it appears Rubio ``won't be standing with Sen. DeMint, Lee and Paul.

``Ultimately what matters is his vote, but there is concern,'' Kremer said. ``All these new members should know that we are watching. If anybody thinks they can play this movement, that's not going to happen. We're watching what they say, what they do.''

Rubio's camp notes the fact that he's not made a final decision about joining the caucus does not mark a shift for the former Florida House Speaker who during the 2010 campaign sought to portray himself as a more of a bridge between the GOP and the tea party. He attended numerous rallies and sought tea party support, but in an interview with CNN in July, said he didn't see the need for a tea party caucus in the Senate, as then-candidate Paul had proposed. ``I don't know what the need for that [tea party caucus] would be, obviously, maybe they feel there is a need for that, or others feel there is a need for that,'' he said. ``I'm more interested in being part of a caucus that would lower taxes in America and create an environment where jobs are going to be created by the private sector.''

Burgos said Rubio's office stays in contact with a number of tea party groups and he's not heard any grumbling.

``Ultimately, he hopes Floridians will judge him on his voting record and his commitment to delivering on the promises he made through the campaign,'' Burgos said. ``He expects people to hold him accountable to that.''

In Florida, Rubio supporters and tea party members said Rubio's voting record will say more about his commitment to conservative causes.

``It would be nice if he joined Rand Paul's caucus, but as long as Marco continues to vote in the way we'd like to see him vote, that's the most important thing,'' said Steve Vernon, vice president of Tea Party Manatee on Florida's west coast. ``As long as his vote and his actions and his word continue to essentially mirror our principals, then we're not really upset.''

Marcos Sendon, president of a tea party group, SFLA Conservative, said he expects Rubio to eventually join the caucus.

He noted that activists were 100 percent behind Rubio's candidacy. ``We were doing events for him when he was 30 points down, when no one wanted to listen to him,'' Sendon said. ``But we know he's been busy, you have to put things in perspective.

``In the final analysis, his joining is secondary to the important issues we sent him up there to solve,'' Sendon said.