The American Civil Liberties Union has issued a warning to an Idaho school district after the district required girls to wear dresses or skirts to their high school graduation ceremony.

Declo High School in southern Idaho has banned graduating girls from wearing slacks during commencement ceremonies set for May 27, a move the American Civil Liberties Union of Idaho said was gender discrimination.

The AP writes, "The Cassia County School District is requiring all female students participating in the high school graduation to wear white or pastel dresses. Male graduating students must wear pants and a tie."

The ACLU said in its statement Tuesday that the dress code violates the equal treatment guarantee articulated in the constitution.

Debbie Critchfield, spokeswoman for the school district, said administrators have requested each of its five secondary schools, including the one in the tiny agricultural community of Declo, to submit instructions they sent to graduating students regarding apparel.

She said the district does not impose standards for graduation per se but broadly asks students to dress appropriately for an occasion that marks a milestone in their educations and lives.

In letters sent on Tuesday, the ACLU asked superintendents of the school's public school districts to announce that graduation dress codes that enforce gender stereotypes will not be enforced this year.