Stephen Heasley and Andrew Borg sat together the night before their wedding and opened a box that was supposed to contain 100 custom wedding programs outlining how their special day was going to go.

The lyrics to their processional song — “Treasure,” by Above and Beyond — were supposed to be on the back.

Instead, Vistaprint allegedly sent 80 pamphlets implying that gay marriage was wrong and that Satan was the “supreme tempter,” according to a lawsuit filed in Boston’s federal court yesterday.

“Rather than send Plaintiffs the custom wedding programs they had purchased, Vistaprint instead sent Plaintiffs literature with hateful, discriminatory and anti-gay messages equating their relationship to Satan’s temptation,” the lawsuit states. “This conduct is morally repugnant and Vistaprint must be held accountable.”

Heasley, 31, and Borg, 39, live in Australia but were married in September in Butler County, Pa. The couple printed out their own programs in time for the wedding, but not until after they came across the stack of pamphlets with messages like: “Fight against Satan’s temptation and pursue what is good,” according to the suit.

“Our memories from that day should have been filled with nothing but love and happiness,” Heasley and Borg said, in a statement emailed to the Herald. “Instead our memories are mixed with vivid memories of the moments where we were taken away from our wedding day, our thoughts filled with the worries and the disturbance that came from receiving the shocking hate mail only hours earlier.”

Attorneys for Heasley and Borg didn’t list an amount they’re seeking from Vistaprint — which has a corporate office in Waltham. However, they did ask that a judge permanently restrain the company “from engaging in any such further unlawful conduct.”

A spokeswoman for Vistaprint said the company was notified about the allegations yesterday and that it “immediately launched an internal investigation.”

“Vistaprint would never discriminate against customers for their sexual orientation,” company spokeswoman Sara Nash said. “We pride ourselves on being a company that celebrates diversity and enables customers all over the world to customize products for their special events.”

The couple’s attorneys say Vistaprint discriminated against their clients “based on their sexual orientation” because they refused to provide them with “the same services as straight individuals.” They also allege that the pamphlets themselves were perceived as a threat.

“This took a great deal of joy out of what should have been the greatest day of their lives,” said Michael J. Willemin, one of the couple’s attorneys. “They want to make sure that this story is told and that people know what happened to them.”