When Ron Anders, an Air New Zealand employee in the United States, won two free air tickets with another airline he decided to visit his mother in Florida with his gay partner.

But his plans came unstuck when Northwest in Los Angeles refused to redeem the tickets because the company did not recognise Mr Anders' partner as his "spouse".

According to Air NZ policy, spouses include same-sex couples, but Northwest have a different definition.

"I was disappointed and angry," Mr Anders, aged 60 of California, told the Washington Blade newspaper this week .

"Northwest wasn't honouring its agreement and not honouring California law."

Mr Anders won the two Northwest tickets at an Air New Zealand staff party in December.

He decided to use the tickets so he and his partner, Patrick Shay, could visit his 89-year-old mother in Florida.

But Northwest refused to redeem the ticket which they said were for a fellow employee, dependent child or "spouse".

Christine Sun, staff attorney for the Lesbian and Gay Rights and Aids Project of the ACLU Foundation of Southern California, told the Blade that Northwest's decision was a violation of California's Civil Rights Act, which mandated "full and equal accommodations, advantages, facilities, privileges or services in all business establishments of every kind whatsoever without regard to sexual orientation or marital status".

She sent Northwest a letter asking the company to redeem Mr Anders' tickets or face potential litigation.

"Because same-sex couples who wish to marry cannot currently do so under California law, using marriage as a criterion discriminates on the basis of sexual orientation," Ms Sun said.

"Northwest's policy also discriminates on the basis of marital status because it does not permit unmarried heterosexual individuals to bring the companion of their choice."

Northwest spokesman Kurt Ebenhoch told the Blade that when the two airlines entered into a ticket swap agreement, Air New Zealand's letter for reciprocal benefits stated the tickets would be for a fellow employee, dependent child or "spouse."

Because of this wording, his company was forced to decline to redeem the tickets.

He said Northwest was in compliance with California law by insisting on the specific "domestic partner" definition when redeeming tickets.

But Air New Zealand spokeswoman Lucy Powell told the newspaper the wording on its letter was "for yourself and your spouse".

"Our definition of spouse includes same-sex couples. I guess it all comes down to the interpretation of 'spouse."

Mr Anders, who receives domestic partner benefits through Air New Zealand, said all he wanted was the prize he won.