Two Chicago students have filed a lawsuit claiming that being forbidden to wear anti-gay t-shirts is a violation of their civil rights.

The Nequa Valley High School pupils, Heidi Zamecnik, 17, and Alexander Nuxoll, 14, are seeking permission from the district court to wear t-shirts bearing homophobic slogans on this year’s Day of Silence on 18th April.

After a discussion between Zamecnik’s parents and school officials led to a rejection of Zamecnik’s request to wear the shirt, the family and Nuxoll decided to take legal action.

On last year’s Day of Silence event, Zamecnik was ordered by a teacher to remove her t-shirt that read “DAY OF SILENCE: STRAIGHT ALLIANCE”.

Another member of staff told her to cross out the latter part of the phrase “BE HAPPY, NOT GAY” on the back of the shirt.

Nuxoll did not attend Nequa Valley School at the time of the incident.

Zamecnik and Nuxoll are being represented by Alliance Defence Fund, the Christian litigation group.

The ADF views gay rights as “an attack on marriage and family values”, particularly same-sex partnerships and allowing gay parents to adopt. The organisation believes that allowing these rights “will ultimately destroy our society”.

They claim that Zamecnik suffered unlawful discrimination and humiliation when told not to wear the t-shirt.

So far the ADF has filed eight other similar lawsuits.

Nate Kellum, an Alliance Defense Fund attorney in Memphis, Tennessee, is representing the two students. According to CBS2Chicago.com, she said: “This is a fundamental First Amendment issue.”

“At its core, this is about students’ fundamental right to express their beliefs, no matter how controversial or whether they are in the minority or not.”

The Day of Silence, an annual event held to commemorate and protest against homophobic bullying, is held in schools across the U.S. Now in it’s 11th year, it is one of the largest student-led demonstrations in the country.