The Netherlands will hold an advisory referendum on a key treaty between the European Union and Ukraine, the electoral council said on Wednesday.

Supporters of the referendum have managed to collect the necessary 300,000 signatures to call a referendum, the council said. Spot checks on the 427,939 signatures indicate only about 1,000 were bogus.

The Geenpeil committee, which campaigned for the referendum, opposes the expansion of the EU and says the association treaty with Ukraine will further damage the Dutch democratic system.

The date for the vote, which will not be binding on the government, is likely to be early next year.

The campaign to hold a referendum was launched by shock blog Geenstijl, think-tank Forum voor Democratie and the Burgercomite EU association earlier this month.

In 2014, the Dutch approved legislation to allow ‘advisory referendums’ on controversial topics, if supporters can gather 300,000 signatures. The Dutch parliament has already voted in favour of the treaty.

Only Dutch nationals aged 18 plus will be able to vote in the referendum.