Five people in northern Alabama have filed a federal lawsuit claiming Texas congressman Ted Cruz is ineligible to run for president.

Cruz was born in Canada to an American mother and a Cuban father.

The U.S. Constitution limits the presidency to 'natural born' U.S. citizens. There are differences of opinion on whether or not the federal courts have established what those two words mean.

Cruz's eligibility has been a frequent campaign theme of Donald Trump, the Republican presidential front-runner.

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THEY WANT TO KNOW: Five Alabama supporters of Donald Trump are asking a federal court to declare that Canadian-born Texas Sen. Ted Cruz is ineligible to run for president

DRUMBEAT: Donald Trump, the Republican presidential front-runner, has said repeatedly that Ted Cruz's citizenship could become a problem for the Canadian-born politician

GETTING IN ON THE ACTION: Minutes after DailyMail.com asked Trump's campaign about the lawsuit, he tweeted a threat to file his own legal action against Cruz

One other lawsuit, filed by an attorney in Texas, has already sought to have a judge untangle the question of Cruz's U.S. bona fides.

But this is the first from voters who argue that their rights would be violated if his name were to be placed on Election Day ballots.

Cruz spokeswoman Catherine Frazier declined to comment when DailyMail.com reached her on Friday.

Trump's campaign manager, Corey Lewandowski, said only that he wasn't aware of the legal action.

'I haven't seen it,' he told DailyMail.com in an email.

But just minutes after DailyMail.com asked for comment, Trump himself tweeted a new shot across Cruz's bow.

'If @TedCruz doesn’t clean up his act, stop cheating, & doing negative ads, I have standing to sue him for not being a natural born citizen,' he tweeted.

The Alabama lawsuit seeks a 'declaratory judgment' from a federal judge 'declaring that Rafael Edward Cruz is ineligible to qualify/run/seek and be elected to the Office of President of the United States of America.'

The plaintiffs, Sebastian Green, Shannon Duncan, Kathryne Spears, Kyle Spears and Jerry Parker are all supporters of Trump's candidacy, according to AL.com.

'Mr. Cruz cannot be a natural born citizen of two (2) countries,' the five argue. 'This would violate elementary rules of logic. Since the Defendant, at the moment of birth, was located in Calgary, Alberta, Canada; he became a citizen of Canada by virtue of it.'

BRUTAL: Trump has gone after Cruz on Twitter over his dual citizenship, which he dissolved in 2014

'Plaintiffs allege that at the time of Mr. Cruz’s birth, the United States could not confer citizenship upon him under any law or legal theory that exists. "Natural born" means native born within the United States or its dominions/territories. Canada is not a territory of the United States. Whether the Defendant’s mother was/is a United State’s citizen is irrelevant.'

The lawsuit states that Cruz's U.S. citizenship was 'conferred by other means' than the situation of his birth.

And 'if Mr. Cruz were allowed to run as a candidate, the Plaintiffs' right to have only lawful and constitutionally qualified candidates to run would be violated.'

Cruz is himself a constitutional lawyer and former solicitor general of Texas, a job where he argued cases before the U.S. Supreme Court.

He has insisted that the 'birther' argument is a non-starter floated for political purposes. He maintains that since he is not a naturalized citizen, he is 'natural born' under the Constitution's definition.

But Trump has repeatedly talked on the campaign trail about Cruz's place of birth, urging the senator to seek the very kind of declaratory judgment the five Alabama plaintiffs are asking for.

Trump has said if Cruz were to become the Republican Party's presidential nominee, Democratic partisans could sue in order to have his candidacy nullified, throwing the GOP into chaos just a few months before the November election.

During a GOP debate last month he conceded that he was making Cruz's citizenship an issue 'because now he's doing a little bit better.'

Since then, Cruz won the Iowa caucuses and placed third in the New Hampshire primary.

VICIOUS: Barbs thrown both ways between Cruz and Trump have morphed into bare-knuckle fighting as the Republican primary season kicks into high gear

In the January 14 debate, Trump joked that 'he's got probably a four or five percent chance' of winning the Republican nomination.

'There's a big overhang,' Trump said, telling Cruz 'there's a big question mark' hanging over his head. 'You can't do that to the party. You have to have certainty.'

'I'm not bringing a suit, I promise, but the Democrats are going to bring a lawsuit,' Trump predicted.

Cruz shot back that 'the legal issue is quite straightforward.

'I've spent my entire life defending the Constitution before the U.S. Supreme Court. And I'll tell you, I'm not gonna be taking legal advice from Donald Trump,' he said.

Two weeks later aboard Trump's private plan on the tarmac in Des Moines, Iowa, the billionaire real estate developer told DailyMail.com that 'Cruz has a real problem.'

'They've got to rule. He's got to go for a declaratory judgment,' he said of the federal courts.

And reflecting on the Cruz campaign' challenge for a one-on-one debate, he said he would debate Cruz – in Canada – 'to give him home-field advantage.'

The following day in New Hampshire he told a rally audience that 'Ted Cruz may not be a U.S. citizen.'

'But he's an anchor baby – No, Ted Cruz is an anchor baby in Canada!' he said on January 29.

'Anchor baby' is a derogatory term referring to children born in the U.S. whose parents are here illegally.

'When you're born in Canada, you're not supposed to run for President of the United States,' Trump crowed. 'Prime minister of Canada? No problem.'

Cruz held dual citizenship until late in 2014 when he laid the groundwork for a presidential run.

'He's a citizen of Canada. And he was a senator from Texas. And he's a citizen of Canada, joint with the U.S. How the hell does that work?' Trump asked during that New Hampshire campaign stop.