Parents in Montgomery County , Maryland , have sued their school district over a policy that prohibits parents from opting their children out of lessons on gender identity and sexual orientation , even for religious reasons.

The plaintiffs, a Muslim family and a Christian family, filed the lawsuit in federal court Wednesday, alleging the district violated Maryland law and their First Amendment rights to the free exercise of religion by not allowing them to opt their children out of lessons that use Pride Storybooks, a series of children's books from the Human Rights Campaign with gay and transgender themes.

The books were first introduced in the classrooms of Montgomery County Public Schools in October, and the lawsuit says that the families repeatedly sought a remedy from school officials before the district declared in March that no opt-outs would be allowed, a reversal of previous policy.

"The School Board’s recent about-face strips away [a] long-standing protection of parental rights," the lawsuit says. "This violates not just Maryland law and Board policy and practice but also the United States Constitution."

The families are represented by the Becket Fund for Religious Liberty, a nonprofit religious freedom legal group. Eric Baxter, the organization's vice president and senior counsel, ripped the school district's policy in a statement.

“Children are entitled to guidance from their own parents, who know and love them best, regarding how they’ll be introduced to complex issues concerning gender identity, transgenderism, and human sexuality," Baxter said. "Forced, ideological discussions during story hour won’t cut it, and excluding parents will only hinder, not help, inclusivity."

Montgomery County Public Schools told the Washington Examiner that the school district does not comment on pending litigation.