American schools have been warned to stop censoring educational lesbian, gay, bisexual and transgender websites.

The American Civil Liberties Union has written to school districts in Missouri and Michigan to warn that filtering such sites violates the constitution.

School districts in ten other states have been asked to clarify their internet policies.

The ACLU won a legal case against two Tennessee school districts in 2009 over the issue but says it is still receiving a steady stream of complaints from students in other states who are unable to view LGBT support websites.

Joshua Block, a staff attorney with the ACLU LGBT Project, said: “Blocking these sites not only discriminates against LGBT viewpoints, but can deny LGBT students in crisis a much-needed lifeline for support.”

The ACLU says that blocking the sites violates First Amendment rights to free speech, as well as the Equal Access Act, which requires equal access to school resources for all extracurricular clubs.

ACLU attorneys say that school policies mean that vulnerable LGBT students may have no way of accessing the support they need, if they are unable to view information at home.

Some schools apparently block support websites like the Gay-Straight Alliance Network and the Gay, Lesbian and Straight Education Network but allow students to view websites aimed at attempting to ‘turn’ gay people straight.

Last month, the ACLU began a ‘Don’t Filter Me’ campaign which asked students to report schools which block gay support websites.

Student Nick Rinehart of Rochester High School in Rochester Hills, Michigan, said: “I couldn’t believe my school would block access to perfectly legitimate websites just because they were about LGBT issues. It’s not fair for the school to try to keep students in the dark about LGBT resources.”

Molly Mendenhall, of Oak Park High School in Kansas City, Missouri, added: “This is legitimate information that we need to know about. We need access to these sites to run our school clubs, to support each other and to understand current events. Schools shouldn’t be putting limits on our education.”

The ACLU says it has given schools until April 4th to respond to its letters.