EU pressure on Hungary has intensified over a new law banning the depiction or promotion of homosexuality for the under-18s.
MEPs are expected to vote shortly for a resolution urging the EU to speed up legal action over Hungary's law.
EU Commission President Ursula von der Leyen said the law was "a disgrace" which contradicted "basic EU values".
Hungarian PM Viktor Orban hit back, saying school policy was a matter for Hungary, not "Brussels bureaucrats".
"Whatever they do, we will not allow [LGBT+] activists into our children's kindergartens and schools," he said.
The EU has the power to reduce budget allocations to a member state seen to have breached the EU's rule-of-law standards.
Critics say the law equates homosexuality with paedophilia and EU leaders have voiced strong criticism, with Dutch Prime Minister Mark Rutte arguing last month that Hungary "has no business being in the European Union any more".
"This legislation uses the protection of children as an excuse to discriminate against people because of their sexual orientation," Mrs von der Leyen said on Wednesday.
What impact will the new law have?
The new rules introduced by Hungary's right-wing government focus on increasing punishment for convicted paedophiles, but an amendment was passed on 15 June banning the portrayal or promotion of homosexuality among under-18s.
While it could affect sex education and advertising, and even stop TV favourites such as Friends or Harry Potter being broadcast until late at night, there are also fears that vulnerable young people could be deprived of important support.
Teaching sex education in schools will be limited to people approved by the government.
It is not yet clear what the penalties for breaching the law will be.
What other rules has Hungary introduced?
Hungary has introduced a number of similar decisions since Prime Minister Orban took power in 2010.
In December 2020, parliament banned same-sex couples from adopting children.
Earlier the same year, the country passed a law preventing people from legally changing their gender.
Hungary also does not recognise gay marriage.
Mr Orban has been widely criticised in the EU, accused of curbing the rights of migrants and other minorities, politicising the courts and media, and tolerating anti-Semitism. He says he is defending Hungary's Christian values in a Europe gripped by left-wing liberalism.