Nearly 50 performers and artists have signed an open letter calling on British rock group Radiohead to cancel its concert in Israel, scheduled for July 19.

The signatories include Roger Waters, the singer-songwriter and co-founder of Pink Floyd, who has been an active advocate for boycotting Israel. Other signees include British filmmaker Ken Loach, British actor Julie Christie, American writer Alice Walker and American rock star Thurston Moore.

Retired South African Archbishop Desmond Tutu also signed the letter. Most of the signatories are British.

"We’d like to ask you to think again – because by playing in Israel you’ll be playing in a state where, UN rapporteurs say, ‘a system of apartheid has been imposed on the Palestinian people,'" the letter states.

"We understand you’ve been approached already by Palestinian campaigners. They’ve asked you to respect their call for a cultural boycott of Israel, and you’ve turned them down. Since Radiohead campaigns for freedom for the Tibetans, we’re wondering why you’d turn down a request to stand up for another people under foreign occupation."

The letter goes on to say: "And since Radiohead fronted a gig for the 50th anniversary of the Universal Declaration of Human Rights, we’re wondering why you’d ignore a call to stand against the denial of those rights when it comes to the Palestinians."

A spokesperson for Radiohead had no comment on the letter, The Guardian website reported Monday. There doesn’t appear to be any real prospect that the group will cancel its concert in Israel, which is set for Tel Aviv's Yarkon Park.

Tens of thousands of tickets have already been sold for the event. The group has played in Israel three times before, with the last gig taking place in 2000.

In reference to Israeli singer Dudu Tassa, whom Radiohead invited to join its U.S. tour and Israeli concert, the open letter ends: "You may think that sharing the bill with Israeli musicians Dudu Tassa & the Kuwaitis, who play Jewish-Arabic music, will make everything OK. It won’t, any more than ‘mixed’ performances in South Africa brought closer the end of the apartheid regime. Please do what artists did in South Africa’s era of oppression: stay away, until apartheid is over."

In the vast majority of cases in which performers sign contracts to perform in Israel and ticket sales begin, the performers are not inclined to cancel concerts in the face of calls to boycott Israel.

Eran Arielli of Narnajah Productions, which is bringing Radiohead to Israel, posted a wry comment directed at Waters and ex-Sonic Youth guitarist Moore on his personal Facebook page, stating that he "wishes Thurston and Roger success on the new album."