But the Dutch vote has been overshadowed by a blazing diplomatic row after the government banned Turkish ministers from addressing a pro-Ankara rally in Rotterdam.
European Union president Donald Tusk said no one could make comparisons between events in Rotterdam and the Nazi period, when the city was "brutally destroyed" by the Germans.
"If anyone sees fascism in Rotterdam, they are completely detached from reality. We all show solidarity with the Netherlands," Tusk told the European Parliament in the French city of Strasbourg.
Tusk repeated the statement in Dutch to applause from MEPs.
European Commission chief Jean-Claude Juncker said he was "scandalised" by the Turkish government's Nazi comments.
"I will never accept this comparison between the Nazis and the (modern-day) governments," Juncker said.
"If you are establishing a comparison with that period this is totally unacceptable. The one who is doing this is taking distance from Europe and not trying to enter Europe," he said.
Turkey resumed long-stalled accession talks with the EU in 2005 but they have made little progress since.
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