More than 100 married couples dressed in their wedding clothes have gathered on the Malecón coastal boulevard to renew their wedding vows and protest against gay marriage being allowed in Cuba.

The protest is the latest in an unprecedented campaign by evangelical churches against elements of the island’s new constitution, which will be put to a referendum next Sunday.

“We’re speaking out in favour of marriage as it was originally designed,” said Bishop Ricardo Pereira of the Methodist Church of Cuba, who emphasised that the event was not political but an “expression of faith”.

“It’s the first time since the triumph of the revolution that evangelical churches have created a unified front. It’s historic,” he added, as drivers honked at women in wedding dresses and unwitting tourists in pink Cadillacs waved.

Bishop Ricardo Pereira of the Methodist Church of Cuba (centre) celebrates during Sunday’s protest. Photograph: Frank Padrón Rojas

Clutching a bunch of flowers next to her husband, Debora Lisset Covas, 32, insisted the demonstration was not homophobic.

“My auntie is a lesbian and I have homosexual friends and colleagues. They are all creations of God and I love them,” she said. “But I don’t want gender ideology to be taught in schools. That’s what happens in other countries once gay marriage is legalised.”

While the state is using television, newspapers and public billboards to urge the population to vote yes to the new constitution, evangelical denominations have run a bullish and unprecedented counter-campaign.

Methodist, Pentecostal, Baptist and Assembly of God denominations have hung three-metre banners on their churches reading: “I’m in favour of the original design. Marriage: man + woman.”

Churches have printed hundreds of thousands of posters and flyers which the faithful have stuck on doors, lamp posts and inside buses.

The church delivered a petition with 178,000 signatures against the legal recognition of gay marriage to Cuba’s National Assembly in October last year – an event without historical parallel on the island.

The church’s highly organised operation has overwhelmed the campaign in support of gay marriage run by the state-linked National Centre for Sex Education (Cenesex) and the island’s LGBT community. Most independent LGBT activists on the island have relied mainly on social media posts.

The Cuban government backed away from enshrining gay marriage in the new constitution after widespread popular rejection. In the public consultations about the new constitution organised in neighbourhoods, workplaces, and universities last year, Cubans made 192,408 comments on Article 68 – which defined marriage as “the voluntary union between two people” rather than a union “between man and woman” as in the current constitution. A strong majority requested that Article 68 be eliminated.

Cuba’s National Assembly announced on Twitter in December that it had eliminated the language “as a way of respecting all opinions”. The final constitution to be voted on by the population waters down the initial wording while leaving the door open to the legalisation of gay marriage in the future.

Analysts expect the yes vote to win comfortably and turnout to be high. But a significant no vote would reflect a political opening on the island coupled with a new generation of leadership that has not yet cemented its authority.

It would also underline how, as elsewhere in Latin America, evangelical Christians have become a political force. Pastors claim that 10% of Cuba’s population of 11 million are now evangelical. The vast majority of them the Guardian has spoken to in recent weeks have said they will vote no on Sunday.

According to electoral authorities, 98% of the Cuban electorate turned out to vote on Cuba’s current constitution in 1976. But in recent years turnout has fallen. While strongly encouraged, voting in Cuba is optional and ballots are secret. Cuba does not allow international observers to audit elections.