The government is facing a high court judicial review over an alleged “large-scale breach” of EU citizens’ rights after they were denied their vote in May’s European elections.

A letter before action has been sent to the de facto deputy prime minister, David Lidington, by the law firm Bindmans, acting on behalf of the grassroots campaign group the3million.

“The government has created a bizarre system … automatically depriving most EU nationals of their voting rights on an annual basis,” said John Halford, the lawyer acting for the3million. He said the requirement to fill in a special form that only assigns the right to vote for one year was discriminatory and did not exist in other EU member states.

“Well over half of EU nationals who are registered to vote in the UK are systematically disenfranchised in this way,” he added.

He said the government had known that its system was stripping EU citizens of their rights since 2014 and had “promised to put it right”, but had failed to do so. “It now needs to accept that is unlawful or face the courts,” added Halford.

The letter accuses the government of four breaches of law including discrimination.

In the UK, EU citizens were required to fill in a UC1 form which remained valid for only 12 months. No such requirement is made in EU law and other member states do not interpret the law in this way, underlining the legal case that the hurdle is exclusively a British invention.

The3million, a grassroots campaign for EU citizens’ rights, is hoping to raise the funds to take the case forward through crowdfunding.

“Many such citizens were deprived of their right to vote because of unlawful systemic flaws in the processes under which the 2019 elections were conducted,” said the letter to Lidington.

The failure of many EU citizens to vote caused shock and outrage in May, and calls followed in the House of Commons for a public inquiry. Guardian data shows that as few as one in 10 EU citizens were able to vote in some local council areas.

Labour MP David Lammy described it as “ugly discrimination” for people who had endured “three years of being insulted, exploited and asked to apply to stay in their own homes” while the head of the electoral commission, Bob Posner, said it was time that its warnings and calls for electoral reform were “properly heard and acted upon”.