The European Court has ruled that Russia discriminated against three gay rights activists who opposed the law. It was adopted in 2013, banning promotion of homosexuality among people under 18.

The law “reinforced stigma and prejudice and encouraged homophobia”, the ruling said.

Under the law, private individuals promoting “homosexual behaviour among minors” face fines of up to 5,000 roubles (£67; $85), while officials risk paying 10 times that amount. Businesses and schools can be fined up to 500,000 roubles.

Homosexuality was decriminalized in Russia in 1993, but anti-gay prejudice is rife.

The Strasbourg court said the fines imposed on three Russian gay rights activists violated Article 10 (freedom of expression) and Article 14 (prohibition of discrimination) of the European Convention on Human Rights.

According to the court, the legislation aimed at curbing promotion of homosexuality was “not clearly defined” and was implemented in an arbitrary way. It “served no legitimate public interest”, the court said.

The three activists had been found guilty for protesting against the law in 2009-2012 – outside a secondary school in Ryazan, a children’s library in Archangel and an administrative building in St Petersburg.

The court rejected the Russian government’s claim that such a law was needed to protect morality.

It found that the government had “failed to demonstrate how freedom of expression on LGBT issues would devalue or otherwise adversely affect actual and existing ‘traditional families’ or would compromise their future”.

Such laws, the judges said, “embodied a predisposed bias on the part of a heterosexual majority against a homosexual minority”.

They ordered Russia to pay each of the activists damages of between €8,000 (£7,000; $8,900) and €20,000.