In the fight for the Republican presidential nomination, South Florida is supposed to be the exclusive turf of two candidates who call the Sunshine State home: Sen. Marco Rubio and former Gov. Jeb Bush.

And while both candidates are racking up endorsements from elected officials in the state, it is one endorsement that neither of them got that is causing the most controversy in Florida.

Manny Roman, the vice-chairman of the Miami-Dade Republican Party who threw his support behind Texas Sen. Ted Cruz over the holiday weekend, told Fox News Latino that it is the "unspoken rule" of GOP officials in South Florida to support only Rubio or Bush in the primary.

He alluded to that rule in the letter to the Miami Herald announcing his endorsement of Cruz, saying that he was doing it despite "pressure to get behind one of the local candidates."

"I had every reason to support Senator [Marco] Rubio instead – he is a well-liked local Republican and my colleague on the faculty at Florida International University. (He teaches politics, while I teach business)," Roman wrote. "However, even in an environment where there is overwhelming indirect pressure to get behind one of the local candidates, Ted Cruz's story and platform break through all the noise."

More On This...

Roman, who identified himself in the letter only as a "Republican activist," referred to Cruz in his letter as "an incredibly talented, principled and unwavering voice for constitutional and limited government. That’s why I’m endorsing him." 

Cruz promptly retweeted the endorsement.

While it is seen as coup for the firebrand Texas lawmaker, possibly raising his hope of winning the battleground state of Florida, it has been called out as bad form – and possibly a violation of the Republican Party of Florida's by-laws – by leading GOP figures.

Miami-Dade GOP chairman Nelson Diaz, who was Rubio's chief legislative aide candidate was Florida House speaker, criticized Roman for the endorsement, calling it not only against the rules for a GOP official.

"It is a violation of party rules (and the loyalty oath we all signed)," Diaz told the Herald, "to use our titles and position to endorse one Republican over another" as well as "a violation of the trust that party members placed in us."

Diaz added that the "The nominee should win by election of the grassroots, in a bottom-up manner, not a top-down push by party leadership. This is why I have stayed publicly neutral in this primary season. It is my hope that other party leaders don't try to put their thumbs on the scales as well."

In an interview with Fox News Latino, Roman – who is now the Cruz campaign's Miami-Dade County chairman but has not stepped down as local GOP vice-chair – said he did nothing wrong endorsing the Texas senator and that it does not reflect the view of the Miami-Dade Republican Party.

"I didn't break any rules," he told FNL. "This is a personal endorsement, and I didn't use my party title when I endorsed Ted Cruz."

Roman added that while GOP leaders in Florida claim to not favor one candidate over the other, it is known that the party is tacitly behind Rubio and Bush. 

"Taking the path of least resistance is the name of the game in South Florida," Roman told Fox News Latino. "There is only one unspoken rule here, and that is you don't support any candidate other than Marco Rubio or Jeb Bush."

Miami-Dade state committee woman Liliana Ros, told Political Cortadito, a Florida political blog, that while a public endorsement by a party official is frowned upon, it is perfectly fine for members to become involved in campaigns by working on phone banks and other election related drives.

"We're not the Communist Party. You can help whoever you want to help," she said. "Except a Democrat, of course."

Ros added that she thinks that Roman was used by the Cruz campaign to gain traction in south Florida and that he should resign from his post because of his endorsement.

"It's too bad. He's a brilliant guy," she said.