Paris is where people – lovestruck locals and tourists alike – kiss. You can hardly take two steps down a rue or grand boulevard without seeing a couple smooching, often in the middle of the pavement.

Carrie and Mr Big chose the Pont des Arts for their kiss in the final episode of Sex and the City and visitors can hire a photographer to capture them recreating Jack Nicholson and Diane Keaton’s kiss outside the Hôtel de Ville à la Something’s Gotta Give. Robert Doisneau’s black-and-white photograph of a couple kissing is perhaps the most famous French kiss, even if it was staged. At the main international station, the Gare du Nord, a parting embrace is de rigueur.

However, it seems that not all kissers are equal in the land of liberté, égalité, fraternité. A train guard from a major railway company has been suspended after allegedly shouting at a lesbian couple that their farewell embrace “cannot be tolerated”. He went on to tell the astonished and humiliated pair that it would have been fine for heterosexual couples to kiss. Now campaigners have insisted that the company, Thalys International, a French, Belgian, German and Dutch rail consortium that has featured a same-sex couple in advertising campaigns, apologises and ensures staff receive equality training.

One of the women on the receiving end of the homophobic rant, Mirjam, 35, from Amsterdam, a member of the organisation All Out, called for gay rights activists to complain to the company in a massive demonstration of solidarity.

“Imagine it. You spent the weekend with your partner in Paris. You say goodbye on the train platform with a hug and a kiss. It’ll be a while until you see each other again. Then an angry train official strides over to stop you kissing – he says it ‘can’t be tolerated’. Humiliating,” she wrote on the All Out site. “My girlfriend and I can’t believe that a Thalys official picked on us just because we’re not a straight couple.”

Later, she told Le Nouvel Observateur magazine: “I couldn’t believe someone was telling me what I could and couldn’t do. I was also shocked because he wouldn’t stop talking, from our arrival on the platform around 8am until the train left 15 minutes later. He certainly spoiled our au revoirs.”

In 2013, Thalys launched an advertising campaign showing couples, including a same-sex couple, embracing, having been reunited by Thalys trains.

“Just like us! But in reality, they didn’t let me kiss my girlfriend on the platform. And they’re staying silent after one of their staff went on an anti-gay rant,” Mirjam wrote. “This isn’t just about this one person’s anti-gay rant, it’s about pushing the company to turn their marketing messages into action and ensure they treat everyone fairly.”

Facebook Twitter Pinterest An image from Thalys International’s same-sex advertising campaign.

A spokeswoman for Thalys confirmed the homophobic incident and said a member of staff had been suspended pending a full investigation. “As soon as we received the complaint we started a preliminary investigation,” Eva Martens, from Thalys, told the Observer.

Agnès Ogier, chief executive of Thalys, said: “Let’s be quite clear: no homophobic word or gesture is tolerated by Thalys. Following the reporting of this serious incident we immediately launched an inquiry with the help of our service provider RailRest, for whom the staff member involved works.” RailRest, is a Belgium-based Thalys International partner company that provides passenger services.

Ingrid Nuelant, deputy CEO at Thalys, said staff received regular training on equality issues: “Thalys has always shown open values without any ambiguity through its publicity campaigns and in its support of pride marches … This incident profoundly affects us and from now will be used as a case history to make our agents more aware.”

On Saturday All Out announced that 60,000 people had signed a petition calling for Thalys to be sanctioned.

Guillaume Bonnet of All Out France told Libération: “The object of this campaign is to say to this company that they can’t run a very gay-friendly marketing campaign and at the same time offer a service that does not treat all customers in the same way. Mobilising people is important to combat everyday homophobia.”