Cosatu general secretary Zwelinzima Vavi and Congress of the People central national committee member Allan Boesak have set aside their political differences to support the Palestinians.
Vavi and Boesak will share a platform at a Palestine solidarity rally in Athlone this Saturday.
Cosatu spokesman Patrick Craven said yesterday that Vavi "is prepared to be part of a group of people, including Boesak, showing their support for Palestine".
The rally will call for "sanctions against the state of Israel".
Cope's head of communications Philip Dexter said he was not aware of the event.
The Palestine Solidarity Group's Eddie Cottle said "Boesak is speaking at the rally as a Christian leader", not a Cope leader.
On Sunday, for the first time, South African Transport and Allied Workers Union (Satawu) members will refuse to off-load a ship from Israel that is scheduled to dock in Durban.
Satawu's Randall Howard said "the union's members are committing themselves to not handling Israeli goods".