Mariano Rajoy, the president of Spain's Partido Popular (People's Party), says the country's gay marriage law is unconstitutional.

Rajoy is vying to become the nation's next prime minister, a post currently held since 2004 by Jose Luis Rodriguez Zapatero, a member of the socialist party. Spaniards will decide on a new leader in 2012.

In an interview Sunday with El Pais, the conservative leader said he does not like the gay marriage law approved by the socialist government in 2005. His party filed a constitutional challenge to the law at its approval.

“I will listen very carefully to the arguments of the Constitutional Court and the people, but I do not like the homosexual marriage act, and I do not think it is constitutional,” he said. “My disagreement is about the use of the word marriage.”

Gay rights groups called Rajoy's statements “outrageous.”

“His words are a clear example of the power in Spain of the Catholic Church, Opus Dei, and PP's homophobia. Homophobia disguised as liberal conservatism,” Tony Poveda, president of Federacion Estatal de Lesbianas, Gays, Transexuales y Bisexuales (FELGTB), Spain's largest gay rights advocate, said.

A 2008 study found that a majority (66%) of Spaniards approve of the law. In its first three years, over 12,000 gay and lesbian marriages were celebrated.