May 1 (Reuters) - The American Civil Liberties Union (ACLU) sued Montana and its Republican House Speaker on Monday, accusing them of violating a Democratic transgender legislator's First Amendment rights by barring her from the House floor after she protested a bill banning gender-affirming healthcare for minors.

Montana's governor signed the bill into law on Friday, two days after the Republican House majority voted to censure Zooey Zephyr and exclude her from the House chamber for the rest of the legislative session for saying in an April 18 floor debate that denying such care would lead to more suicides.

"If you vote yes on this bill... I hope the next time there's an invocation when you bow your heads in prayer, you see the blood on your hands," Zephyr said in the debate. Republicans accused her of violating decorum.

The ACLU filed its lawsuit on Monday in Montana's First Judicial District Court in the County of Lewis and Clark on behalf of Zephyr and four of her constituents, alleging that barring her from the House floor for her comments "extinguishes a vital part of the job her constituents elected her to do."

Montana House Speaker Matt Regier did not immediately respond to requests for comment.

After the Republican supermajority in the legislature silenced Zephyr within the chamber until she apologized for her April 18 comments, her supporters protested at the statehouse on April 24. Seven demonstrators were arrested.

Montana ACLU legal director Alex Rate said in a news release announcing Monday's lawsuit that Regier had "unfairly, unjustly, and unconstitutionally" silenced Zephyr's constituents by silencing her, and called his actions "a direct threat to the bedrock principles that uphold our entire democracy."

A Republican supermajority in the Tennessee statehouse earlier this month expelled two Democratic lawmakers who had protested in support of gun control, drawing national attention. Their county legislatures promptly reappointed them to their seats.
Reporting by Julia Harte; editing by Donna Bryson and Bill Berkrot

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