A landmark legal hearing is preparing to rule on whether veganism is a “philosophical or religious belief” and so protected in law.

Jordi Casamitjana claims he was sacked as a researcher for the League Against Cruel Sports after raising concerns that its pension fund was being invested in companies involved in animal testing.

He claims he was unfairly disciplined for this and that the decision to dismiss him was because of his philosophical belief in ethical veganism.

But the league said it sacked Mr Casamitjana for “gross misconduct”.

Dietary vegans and ethical vegans both eat a plant-based diet, but ethical vegans also try to exclude all forms of animal exploitation including not wearing clothing made of wool or leather and not using products tested on animals.

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Mr Casamitjana’s lawyers say ethical veganism satisfies the tests required for it to be a philosophical or religious belief, which would mean it is protected under the Equality Act 2010.

For a belief to be protected, it must meet tests including being worthy of respect in a democratic society, not being incompatible with human dignity and not conflicting with fundamental rights of others.

The act makes it unlawful for an employer to treat an employee less favourably than others because of their religion or belief.

Slater and Gordon solicitor Peter Daly, who is acting for Mr Casamitjana, said ethical veganism was a philosophical belief held by a significant portion of the population in the UK and around the world.

“This case, if successful, will establish that the belief entitles ethical vegans to protection from discrimination,” Mr Daly said in a statement.

Mr Casamitjana said: “Although the manner in which I was dismissed was intensely distressing for me, some good may come of it if I am able to establish this valuable protection for all ethical vegans.”

The dismissal came after he gave colleagues details of the charity’s pension funds, revealing that some invested in certain companies involved in animal testing. He claims he was whistleblowing.

But lawyers for the charity say he defied managers’ rules. The league says that in 2015, pension guidelines changed, so it was unable to automatically enrol new staff in an ethical scheme. It rectified this when it was made aware of the rule changes.

A spokesperson said if they dismissed staff on the grounds of being vegetarian or vegan they would have few staff left and they were not contesting his claim that veganism should be protected.

She referred to a statement from 2018, saying: “The discussion about veganism being a ‘philosophical belief’ is a thought-provoking one which many of our staff will be interested in; however, this debate has absolutely no connection with why Mr Casamitjana was sacked.”

The statement went on: “Mr Casamitjana was not dismissed because he raised concerns about the pension, either internally or externally, so our view is that there is no substance to his claims that he was ‘whistleblowing’.”

The charity said the reason for his dismissal was confidential but said it was sad that a former employee, who was passionate about protecting animals, was taking action against one of the UK’s most vegan-friendly employers.