The head of French President Emmanuel Macron's political party has threatened to withdraw support for one of its own candidates in regional elections after she wore a headscarf for a campaign poster. The threat from Stanislas Guerini, who helped to found Mr Macron's centrist movement in 2016, caused a rift within the governing Republic on the Move (LREM) party, with some MPs voicing open criticism. Mr Guerini reacted on Monday to the election poster for Sara Zemmahi, an engineer who is standing for the party in the southern city of Montpellier in regional elections on June 20 and 27. The picture of Ms Zemmahi, who is shown smiling in a white headscarf alongside three party colleagues, was tweeted by the deputy of France's far-right National Rally party, Jordan Bardella. "Wearing ostentatious religious symbols on a campaign document is not compatible with the values of LREM," Mr Guerini wrote late on Monday in reply to Mr Bardella. "Either these candidates change their photo or LREM will withdraw its support." Government spokesman Gabriel Attal backed the ultimatum on France Inter radio on Tuesday. Mr Attal said that "legally, nothing prevents someone standing in an election from displaying a religious symbol, in this case a headscarf". But he said it was a "political choice" to have candidates who did not display their religious beliefs. Analysts say Mr Macron has shifted to the right in recent months, with security and immigration set to be key issues in presidential elections next year. His government is in the process of passing legislation to crack down on what he has termed "Islamist separatism". This would give the state more power to vet and disband religious groups judged to be threats to the nation. Polls show support for National Rally leader Marine Le Pen at historic highs as the main rival to Mr Macron, who was elected in 2017 promising to be neither left nor right. France has a strict form of secularism called "laicite", which was born from more than a century of struggle for power between the state and the Catholic Church. The law obliges state workers to respect strict religious neutrality and prohibits them from wearing religious symbols, such as a Muslim headscarf, a Jewish yamulka or a visible Christian cross. But nothing prevents local elected figures from displaying their religion or prevents citizens from freely practising their faith. One of Ms Zemmahi's fellow candidates in Montpellier said she should not be judged by what she chose to wear. "I see Sara's abilities, I don't see what she's wearing," Mahfoud Benali, who is pictured with Ms Zemmahi on the poster, told France 3 television. Local LREM National Assembly deputy Coralie Dubost also condemned Mr Guerini's ultimatum. Ms Dubost described Ms Zemmahi as "a young woman engineer who does hours of charity work and who is involved in a party that has progressive values". She said there was "a place for her with us", regardless of whether she wore a headscarf. In a meeting of deputies on Tuesday, Mr Guerini reportedly admitted that replying directly to the far right was "an error". "If some people have been upset, then I'm sorry," he said. Last September, a Muslim student representative was boycotted by several right-wing deputies and one from Mr Macron's party when she attended a parliamentary hearing wearing a headscarf. Debate has raged for years in France about whether the headscarf is a political statement, or simply a cultural sign and clothing choice adopted by many Muslim women. <strong>More on France</strong>