When a same-sex couple excitedly opened their wedding programs on the eve of their Pennsylvania ceremony, they were horrified by what they found inside the package.

“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,” according to a new lawsuit targeting the web-based printing company.

The plaintiffs, Aussies Stephen Heasley and Andrew Borg — who married at a hillside ceremony in Butler County, Pa., in September — added in a statement, “Our goal is to hold Vistaprint accountable for the harm they have caused … and to send a message that there will be consequences for acts of hate perpetrated against others.”

Heasley, 39, and Borg, 31, had ordered 100 blue and gold programs for $79.49 that included the lyrics to their processional song, “Treasure” by Above and Beyond. They had gotten engaged on the same day they saw the English electronic-dance music group perform “Treasure.”

But “when Mr. Heasley and Mr. Borg opened the Vistaprint package, they were horrified to find that Vistaprint had not shipped their customized wedding package,” according to their Massachusetts federal suit, which also targets the “John Doe” responsible for the odious incident.

“Instead Vistaprint shipped them approximately 80 copies of a discriminatory pamphlet entitled: ‘Understanding Temptation: Fight the good fight of the faith.’”

“The pamphlets — plainly sent to threaten and attack Mr. Heasley and Mr. Borg because they are gay — warn that ‘Satan entices your flesh with evil desires,’” the suit says.

The betrothed “were both emotionally devastated by Vistaprint’s intimidating and discriminatory conduct,’’ they say in court papers.

They had to print their own programs at an additional cost, the suit says.

They’re suing for unspecified damages.

“This case presents a particularly egregious example of a company refusing to provide equal services to members of the LBGTQ community,” said their lawyer, Michael J. Willemin, of the law firm Wigdor LLP.

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

“We have just been made aware of this incident in the last few hours. We understand how upsetting it would be for anyone to receive materials such as these the night before their wedding and we have immediately launched an internal investigation,” the spokesperson added.

The suit comes a month after the US Supreme Court heard a case about a Colorado baker who refused to make a custom wedding cake for a same-sex couple.