A key clause in EU copyright rules complies with the bloc's regulations, an adviser to Europe's top court said on Thursday, dealing a blow to Poland which had brought the legal challenge, Reuters reports.

Adopted two years ago, the landmark rules seek to ensure a level playing field between the European Union's trillion-euro creative industries and online platforms.

They require companies such as Alphabet unit Google and Facebook to pay fair compensation for using the works of European authors and publishers.

A central provision, Article 17, would force sharing platforms such as YouTube and Instagram to filter copyrighted content. It is backed by the creative industry, pitting artists and news publishers against tech companies, internet activists and consumer groups.

Poland said the filter requirement could lay the foundation for censorship and asked the Court of Justice of the European Union (CJEU) for it to be annulled, the first legal challenge to the copyright rules.

CJEU Advocate General Henrik Saugmandsgaard Øe rejected Poland's arguments and said the Article is compatible with the freedom of expression and information guaranteed in the EU Charter of Fundamental Rights.

"While Article 17 entails an interference with freedom of expression, that interference satisfies the conditions laid down in the Charter of Fundamental Rights," he said in a non-binding opinion. He said regulators had provided safeguards to minimize the risk that online platforms may over-block lawful information with their filters.

The CJEU, which will rule in the coming months, follows four out of five recommendations by its advisers.

The European Commission last month sought to defuse the row over Article 17 by defining its scope but drew condemnation from EU broadcasters and internet activists worried about the danger of censorship.