Sixteen Republicans elected to represent Massachusetts at the national convention in Tampa next month have filed a formal challenge with the Republican National Committee, saying they were unfairly disqualified based on state GOP leaders’ concerns about their fealty to presumptive presidential nominee Mitt Romney.

The group of delegates — originally supporters of Republican presidential candidate Ron Paul — were elected in April caucuses at which they unexpectedly defeated many of Romney’s chosen delegates, but they have been since disqualified by state party officials.

“In short, the Massachusetts Republican Party changed the rules,” the delegates wrote in a letter to the national committee.

The filing sets off a formal but uphill process for the would-be delegates, who hope to convince national party officials that they are being unfairly excluded from the Republican National Convention, to be held Aug. 27-30 in Tampa. An RNC committee is expected to consider the challenge by mid-August, but the party is not expected to make a decision until the week before the convention.

Any appeal to that decision could be considered by the convention’s credentials committee when the event begins.

The legal counsel for the Republican National Committee could not be reached on Friday and a committee spokeswoman declined to comment. A spokesman for the Massachusetts Republican Party referred calls to the RNC.

“This matter is currently before the RNC and we await their decision,” spokesman Tim Buckley said.

In their letter, the so-called liberty delegates say they were duly elected in April, but disqualified after failing to provide timely affidavits pledging their support to Romney. They argue that the affidavits were not called for in state or federal rules and they received them “less than one week before an arbitrary deadline” to return them notarized — during the Memorial Day weekend.

Some met the deadline, but others missed it and many filed a different version of the affidavit, promising only to follow the state's rules, rather than pledging their support to Romney by name.

As a result, the state GOP decided there was just cause to disqualify the group of delegates. They replaced the elected delegates with 16 others, some of whom had been defeated at the caucuses and others who had not run, according to the challenge, leading liberty candidates to cry foul.

One national Republican leader familiar with the challenge said he believes that the Paul supporters do not intend to support Romney, but to make mischief at the convention, as evidenced by their unwillingness to provide affidavits pledging their support.

“If they’re not willing to say that — that’s their prerogative — but clearly they’re not Mitt Romney delegates,” said the leader, who asked not to be named because of the legal challenge.

Supporters of Paul, a Republican congressman from Texas who has stopped campaigning for his party’s nomination, still hope to have a large presence at the convention in order to elevate Paul’s libertarian message and influence the party’s platform. Among Paul’s agenda items is a measure to “audit the Fed” — demanding increased transparency at the central bank — that overwhelmingly passed the House last week.

While their challenge plays out, would-be delegates are uncertain whether to follow through with their travel plans. “It’s a really awkward situation. A lot of them are trying to get guest passes with the other liberty delegates,” said Brad Wyatt, one of the delegates who was eliminated. “We’re cautiously optimistic that we’ll get some good decisions.”

Stephanie Ebbert can be reached at ebbert@globe.com. Follow her on Twitter @StephanieEbbert.

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