A longtime attorney in Republican presidential candidate Ted Cruz’s hometown of Houston has filed a federal lawsuit that questions the Canadian-born lawmaker’s eligibility to be president of the United States.

Newton Schwartz asked the Supreme Court in a 28-page complaint to decide whether Cruz – who was born in Calgary, Alberta to an American mother and a Cuban father – would be violating the Constitution's "natural born citizen" requirement if he won the presidency.

"I have an uncertainty about it and no one has brought this up before," Schwartz told Fox News Latino. "My doubts come from the wording of the Constitution."

Cruz argues that because his mother is American, he became a U.S. citizen at birth. But the Supreme Court hasn't previously considered the eligibility question.

Presidential rival Donald Trump has repeatedly questioned Cruz's eligibility to the White House.

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The pair squared off during Thursday night's Republican debate. When Trump again raised the issue, Cruz shot back that though the Constitution hasn't changed recently, his polling numbers have — driving Trump's "birther" concerns.

"There's a big question mark on your head and you can't do that to the party," Trump said. "You have to have certainty." He is urging Cruz to ask courts for a declaratory judgment to settle the matter."

Cruz cited the widely accepted legal principle that anyone born to an American parent is a natural-born citizen, regardless of where the child is born. He says Trump is basically claiming that a natural-born citizen would have to be born in the United States to two parents who were also born in the United States.

That standard, Cruz said, would disqualify several candidates. Among them Donald Trump, whose mother was born in Europe.

"You're an American, as is everybody else on this stage," Cruz said. "I would suggest we focus on who is best prepared to be commander-in-chief."

Schwartz said that while Cruz should have himself taken the issue to court earlier, he believes that his suit will help settle the issue once and for all.

"Good politics would have been to take it to a court in Houston to decide that he is a citizen," he said. "It would have been better to have gotten it done early than a few weeks before the Iowa caucus."

The Associated Press contributed to this report.

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