Washington CNN —  

Marco Rubio may be gone, but he’s not all the way out.

State Republican Party chairmen in places where the Florida senator won delegates – necessary to secure the party’s presidential nomination – say Rubio’s campaign has contacted them saying he wants to hold on to that support for now.

His decision to try to keep his 173 delegates could make Donald Trump’s path to the 1,237 needed to clinch the nomination just a little bit tougher.

“Of course, he’s no longer a candidate and wants to give voters a chance to stop Trump,” said Alex Burgos, a Rubio spokesman.

A source familiar with the strategy told CNN the move to hold on to delegates was designed to deny Trump from winning the nomination on the convention’s first ballot and assist rival Ted Cruz.

Trump’s opponents – including the many Republican and conservative leaders gathered in different anti-Trump groups – are hoping to deny him a win on the first ballot and block his path to the nomination.

Tennessee Republican Party Chairman Ryan Haynes told CNN he received a letter Monday from Rubio’s campaign stating that his decision to suspend his campaign was “not intended to release any national convention delegates bound to me as a result of the 2016 delegate selection process that took place in your state.”

“It is my desire at this time that the delegates allocated to me by your rules remain bound to vote for me on at least the first nominating ballot at the national convention,” said the letter, which was signed in Rubio’s name.

RELATED: 7 things you need to know about a contested convention

In Tennessee, state rules offer delegates pledged to a candidate who has withdrawn from the race “the right to attend the convention.” But in the event they should choose not to travel, the state GOP chairman has the power to select a replacement.

Rubio’s strategy already pulled back a handful of delegates from both Trump and Ted Cruz in Alaska.

Alaska Republican Party Chairman Peter Goldberg said he had reallocated the delegates in his state to 14 each for Trump and Cruz after Rubio dropped out. Goldberg said his reallocation was based on lawyers’ advice to divide them proportionally between Trump and Cruz.

But after receiving the letter from Rubio and consulting with his lawyers, he decided to make the five delegates Rubio won in Alaska bound to him for the first ballot – and then divide them between Trump and Cruz on the second ballot.

If Trump does not win 1,237 delegates ahead of July’s Republican National Convention, a battle is likely to ensue.

Delegates are committed to voting for the candidate who won their support in a state contest on the first ballot at the convention, but they are free to support other candidates after either the first or second round of balloting (depending on the state’s rules.) In both Alaska and Tennessee, for instance, the delegates are committed – or bound – to Trump, Cruz or Rubio for two ballots, but after that they are up for grabs.

As the numbers tighten, the fight for Rubio’s 173 pledged delegates – and to a lesser extent, the nine won by Ben Carson and Jeb Bush’s four – is expected to heat up, giving the Florida senator, who suspended his campaign on March 15, renewed influence on the race.

RELATED: Can Trump get to 1,237 delegates?

The rules guiding where those delegates end up after the first ballot vary across the states, with some bound to their initial winner through the convention, others automatically unbound when a candidate drops out and others reallocated based on results from the initial primary or caucus.

Trump threatened a lawsuit after 10 of the state’s uncommitted delegates, including five who had been bound to Rubio, indicated they would support Cruz.

A call to the Louisiana Republican Party seeking information about what would happen with the five delegates Rubio won was not immediately returned Tuesday evening.

CNN’s Manu Raju and Tal Kopan contributed to this report.