Costa Rican lawmakers opposed to gay rights say they were duped into approving a bill which could extend some benefits associated with marriage to gay and lesbian couples.

According to daily La Nacion, the language was tucked away in a broader youth social services bill which touches on marriage.

The Legislative Assembly approved the measure on Monday. On Tuesday, social conservatives called on President Laura Chinchilla to veto it. However, Chinchilla, the nation's first female president, has previously signaled support for such rights, the Tico Times reported.

Jose Maria Villalta, a member of the leftist Broad Front Party, inserted the language into the bill.

“During the discussion in the first debate, we explained that the Law of Young People should be interpreted with this sense of opening to gay people and no one objected,” Villalta is quoted as saying by La Republica.

In criticizing the bill, Justo Orozco, a member of the conservative National Renovation Party, likened being gay to an addiction.

“That preference is not right,” he said. “It's a stunted development of sexual identity. It can change like alcoholism, tobacco addiction.”

Other lawmakers said that the bill could not establish civil unions for gay couples because Costa Rican law defines marriage as a heterosexual union.

“The reference that is here is for heterosexual partners,” said Carlos Avendano, a member of a different conservative party, the National Restoration Party.