A Monday rally will urge Prince William and his fiancee Kate Middleton to support gay marriage.

At the rally to be held outside Buckingham Palace, members of Equal Love, the gay marriage campaign helmed by UK rights activist Peter Tatchell, will deliver a giant wedding card to the couple.

“We plan to deliver a giant wedding card to William and Kate. As well as wishing the royal couple every happiness, we will highlight the fact that William and Kate can marry, but same-sex couples can't,” wrote Tatchell at the group's blog.

Currently, gay couples in the UK can enter a civil partnership, but not marriage, and heterosexual couples are banned from seeking a civil partnership.

“Kate and William had a choice,” Tatchell added. “They could get married, or not.  Same-sex couples don't have this choice. We are banned from marriage by law. We urge Kate and William to support marriage equality: the right of same-sex couples to get married. Their support would mean a lot. They take for granted the right to marry. Marriage is something that many lesbian and gay couples want but cannot have.”

At the group's Facebook event page, nearly 300 people have indicated they'll attend the rally.