British academics have been warned that controversial plans to boycott Israeli universities would be illegal.
Members were urged to consider the "moral implications" of Israeli links
The University and College Union (UCU) agreed to debate cutting all links with such institutions because of concerns over Palestinian access to education.
But a UCU spokesman said the latest legal advice to the union said any boycott of Israel "would be unlawful" and could not be implemented.
Jewish leaders and the government have condemned any such boycott of Israel.
At its annual conference in May, the UCU was urged to consider the "moral implications" of links with Israeli universities and voted in favour of a motion to further discuss an all-out boycott.
The motion was passed by a large majority despite opposition from the union's general secretary, Sally Hunt.
But legal advisors have said such a boycott would be "beyond the union's powers and unlawful for the union".
"The use of union funds directly or indirectly to further such a boycott would also be unlawful," they added.
UCU said this meant it would have to cancel a planned series of debates around the country on the boycott.
Ms Hunt said she hoped the decision would allow the union to move forward and focus on representing its members.
"I believe if we do this we may also, where possible, play a positive role in supporting Palestinian and Israeli educators and in promoting a just peace in the Middle East."
Former prime minister Tony Blair had urged academics to abandon their discussion of a boycott in June.
Later in the month, England's Higher Education Minister, Bill Rammell, flew to the Middle East to speak to the Israelis and Palestinians and soothe tensions caused by the boycott call.