Griffiths, the club's attorney, did not return phone calls.
But in his argument to the court, Griffiths referred to a 1990 case in which a landlord refused to rent to a woman and her fiancé. The Minnesota Supreme Court reversed the lower court's discrimination finding.
"The court held that, absent express legislative guidance, the term marital status would not be construed in a manner inconsistent with the state's policy against fornication and in favor of the institution of marriage," Griffiths wrote.
"The fact is they've got a product that they only sell to heterosexuals, and that's a problem," Duran countered.
A check of other health clubs found that most don't specify what defines a family.
Jason Thunstrom, spokesman for Life Time Fitness, a national chain based in Minnesota, said a couple can get a reduced rate if they can demonstrate proof of joint financial obligation, such as a mortgage or checking account.
In the Twin Cities, YMCAs, YWCAs and the Sabes Jewish Community Center in St. Louis Park allow same-gender family memberships.
"The Sabes JCC is an inclusive agency," said Stuart Wachs, executive director. "We would absolutely allow, and do allow, same-sex couples for couple and/or family memberships. Inclusion, be it sexual orientation, religion, financial ability, is an integral part of our mission."
Said Duran, "Almost all companies say, 'If you live together, no problem, we'll take your money.'"
Club membership divided
Kathy Raffel, who has a family membership at the Rochester Athletic Club, said she was fine with the Monsons getting one, too.
"If the law finds that they should have one, then I'll welcome them to the club," she said.
Former member Duane Quam agrees with the club's position.
"[The Monsons] are not being denied service," he said. "The club is following a legal definition of family that has been backed by a wide variety of people, [including the late Sen.] Paul Wellstone."
Those who know the Monsons are not surprised they are fighting the club's decision.
"[Amy Monson] is a phenomenal teacher and a phenomenal person," said former student Alyssa Offutt, who graduated from Mayo in June. "She brings so much energy and creativity into the classroom. You know she really cares about her students."
Offutt wrote an editorial for the school newspaper supporting the Monsons when they filed the suit in March.
"I don't think there is a textbook definition of a family, or that the RAC can define a family," Offutt said. "I think [the Monsons] are just as much a family as any family I've seen."