Despite historically supporting gay rights, Marriott has come under fire for hosting an ex-gay therapy conference.

An All Out and SumOfUs are working together on a petition to urge Marriott to cancel its hosting of the conference by the National Association of Research and Therapy of Homosexuality (NARTH).

The practice of gay “cure” therapy has been widely condemned by medical practitioners and institutions, including the American Psychological Association which said that such therapy could have “serious potential harm to young people”.

Many health organisations condemn the practice, including the American Academy of Pediatrics, American Medical Association, American Psychiatric Association and the World Health Organisation.

Those opposed to it have agreed that it can cause serious and long-term harm.

Worldwide hotel chain Marriott International announced in August that it is to sponsor the 2014 Gay Games, in Ohio, despite being owned by a Mormon family, and the religion considering homosexuality a sin.

The hotel chain previously experienced a boycott from the LGBT community because it supported a 2008 campaign to amend Californian legislation to define marriage as between one man and one woman.

At the time, however, chairman Bill Marriott wrote that the company was built on “respect and inclusion”, and that he had never directly donated money to the cause.

He said: “I am very careful about separating my personal faith and beliefs from how we run our business.”

Marriott was one of many big brands to come out in support of a Supreme Court decision on equal marriage, back in June, and had previously joined a coalition of companies pushing for the repeal of the Defense of Marriage Act.

A federal appeals court in the US recently upheld a ban in the US state of California on the extremely controversial practice of gay ”conversion” therapy for minors.

Last September, campaigners and medical professionals welcomed California Governor Jerry Brown’s decision to ban teenagers from accessing discredited treatments that seek to reject an LGBT identity.

New Jersey Governor Chris Christie in August signed into law a ban on gay conversion therapy for those under 18 years of age.