SAN JOSE, Costa Rica -- Conservative Costa Rican lawmakers are mortified that they may have accidentally approved language making same-sex unions legal when they passed a piece of legislation this week.

President Laura Chinchilla on late Thursday signed the bill governing social services and marriage regulations for young people.

The mostly conservative members of Congress didn't notice that the final version of the bill had changed earlier language that defined marriage as a union between a man and a woman.

After realizing they had approved a bill that "confers social rights and benefits of a civil union, free from discrimination," the lawmakers asked Chinchilla to veto the new law. She has refused.

Conservative lawmakers say they'll launch a legal challenge to the new law which they say goes against family values.