A Jewish politician from Britain’s Labor Party said the views of Jeremy Corbyn, the frontrunner to head the party, are cause for “serious concern.”

Ivan Lewis, the shadow, or minority, party cabinet minister who is also a former chief executive of the Manchester Jewish Federation, urged his party not to vote for Corbyn.

“Some of [Corbyn’s] stated political views are a cause for serious concern,” Lewis said in letter to his local party members on Friday, according to the Guardian. “At the very least he has shown very poor judgment in expressing support for and failing to speak out against people who have engaged not in legitimate criticism of Israeli governments but in antisemitic rhetoric.”