The Norwegian Confederation of Trade Unions (LO) went against a recommendation from its leadership and voted 197 to 117 in favour of an international economic, cultural and academic boycott against Israel because of the current impasse over the Palestine issue.
LO, which also called for Norway to recognise a Palestinian state according to the 1967 borders, was criticised by the government.
"Norwegian government strongly opposes Norw Labour Union's decision: #boycott of #Israel. We need more cooperation and dialogue, not boycott," Foreign Minister Borge Brende wrote on Twitter.
Israel's embassy in Oslo said it "condemns in the strongest terms" the boycott.
"This immoral resolution reflects deeply rooted attitudes of bias, discrimination and double standard towards the Jewish state," ambassador Raphael Schutz wrote in an email to AFP.
Noting that LO had also called for the dismantling of a barrier erected by Israel separating it from the Palestinian territories, Schutz said that "by adopting these positions LO placed itself shoulder to shoulder with the worst enemies of Israel".
Norway hosted Israeli-Palestinian peace talks in the early 1990s that led to the now-defunct Oslo accords.