Lamba Legal and the other groups have been careful and deliberate in challenging marriage bans, and they have a successful track record. They won the marriage case in the California Supreme Court -- which Proposition 8 partly overturned -- and helped win marriage rights in other states.

Fearing a defeat in the conservative-dominated U.S. Supreme Court, the groups have chosen to litigate in state courts. State high courts have the final word on whether marriage laws violate state constitutions. Proposition 8 amended California's Constitution.

Kate Kendell, head of the National Center for Lesbian Rights, said opposition to the groups' intervention, "given the enormity of what is at stake, is perplexing."

"This case is about our community and not any transient misunderstanding or disagreement among the lawyers," Kendell said. "The stakes of this case for the entire community are legendary, and this is an all-hands-on-the-deck moment."

The groups want to bring more members of the gay community into the case, which their detractors say would cost time. Olson hopes to get the legal challenge to the U.S. Supreme Court in two years.