The National Organisation for Marriage is seeking permission to defend Oregon’s same-sex marriage ban in court, after the state declined to defend the law.

In February, Oregon’s Attorney General, Ellen Rosenblum declined to defend the ban, arguing that it would not stand up to a constitutional challenge.

The lack of opposition from the state had meant that when the case appeared before the court, it would have done so unopposed.

However, anti-gay group the National Organisation for Marriage has now filed a motion to intervene in the case, to oppose the ban in lieu of the state.

Brian Brown, the group’s president, said: “Marriage in Oregon is worthy of defense, yet the Attorney General has abandoned her duty to defend the marriage state constitutional amendment enacted overwhelmingly in 2004 and in effect has switched sides.

“We are working to protect the interests of our members who support true marriage against a collusive lawsuit that has the state joining with the plaintiffs against the interests of our members, and the state’s voters.”

The case to overturn the ban, brought by the American Civil Liberties Union on behalf of several same-sex couples, is scheduled to be heard in federal district court in Eugene tomorrow.

John Eastman, who is seeking to be NOM’s lead legal counsel in the case,  filed the motion to intervene today.

He said: “It is precisely for this reason that federal law has a strong premise that organizations like NOM should be able to intervene to defend the interests of their members who cannot adequately defend those interests themselves.”

David Fidanque of the Orgegon ACLU said the his group would oppose the eleventh-hour motion from NOM, “because it is coming at such a late date.”

NOM is holding an anti-gay fundraising gala next month, with tickets costing up to $15,000.