British Labour party leader Jeremy Corbyn is under fire over an undeclared donation by a Palestinian Arab group whose founder once praised Hamas, the British Observer reports.

The group, Friends of Al-Aqsa, held a fundraising dinner at which it collected £10,000 for Corbyn’s last leadership campaign, documents seen by the newspaper revealed.

The organization gave Corbyn’s team a cheque for £10,000 in August 2015, but the gift has never been made public.

Corbyn’s campaign said it did not declare the donation because its bank subsequently rejected the cheque as it was made out to the wrong person.

Any donation above £7,500 should be declared to the Electoral Commission, noted the Observer.

A spokesman for Corbyn was unable to explain on Saturday what then happened to the cash raised, saying “I’m told a second cheque may have been sent but this was not received by the campaign.”

Friends of Al-Aqsa was founded by Ismail Patel in 1997 with the goal of highlighting what is described as “the plight of Palestinians in Israel”, although it has been caught up in a series of controversies.

In 2009, during the counterterrorism Operation Cast Lead in Gaza, Patel reportedly told a rally, “Hamas is no terrorist organization. The reason they hate Hamas is because they refuse to be subjugated, occupied by the Israeli state, and we salute Hamas for standing up to Israel.”

Patel was also a spokesman for the British Muslim Initiative, an organization that the Daily Telegraph has claimed has links to Hamas.

A spokesman for Friends of Al-Aqsa declined to comment on the donation to Corbyn’s campaign, according to the Observer.

John Woodcock, Labour MP for Barrow and Furness, responded to the revelations and said. “These revelations raise incredibly serious questions about the probity of the campaign’s finances and the relationship between Mr. Corbyn and this organization. We need Mr. Corbyn to give full and frank explanations.”

Corbyn has already been criticized for calling Hamas and Hezbollah his “friends” and for outright refusing to condemn those two terrorist organizations despite being urged to do so by local Jewish groups.

Letters that were exposed in June also reveal that Corbyn in the past described Israel’s politicians as “criminals,” called for them to be banned from Britain and for trade sanctions to be imposed on the Jewish state.

Corbyn was accused by Jewish community representatives as well as senior Labour members and backers of generating an atmosphere that encouraged expressions of anti-Semitism due to his comments.

Corbyn has disputed this, although last month he also said he regrets calling Hezbollah and Hamas his “friends.”