The debate over whether Canadian-born Ted Cruz is eligible to be US president is moving from the campaign trail to the courtroom.

Lawsuits challenging the Texas Republican’s eligibility for the ballot have been filed in states including Illinois, New York and Alabama.

Fellow candidate Donald Trump has also threatened to sue over the issue.

Cruz and legal experts say he is eligible because his mother was a US citizen when he was born.

The Illinois plaintiff is pharmacist and lawyer Lawrence Joyce. He says he fears if Cruz becomes the Republican nominee, Democrats will get him kicked off the ballot in some states or Cruz will be forced to drop out and Republicans will replace him with a moderate candidate.

Joyce says he backs Ben Carson but is acting independently.

A Cook County judge set a hearing for 1 March on a motion to dismiss the suit filed by Cruz’s lawyer. By then, ballots for Illinois’s 15 March primary will be printed and early voting under way.

Asked about his eligibility during a CNN town hall event this week, Cruz said by law he has been a US citizen since the day he was born.

The Indiana election commission on Friday rejected a challenge to whether Cruz may remain on the state’s 3 May primary ballot.

Cruz won a similar ballot challenge in New Hampshire in November.