Attempts by Ed Miliband to reform Labour's links with the trade unions could be spurring grassroots opposition to Israel, it has been claimed.
Supporters of Israel believe the Labour leader's disputes with the unions over funding and voting rights have partly led to a raft of vehement anti-Israel motions being tabled at two major conferences in the coming weeks.
Trade unionists are expected to accuse Israel of ethnic cleansing and call for refreshed boycott attempts as part of their backlash against Mr Miliband's policies.
Mr Miliband and his Shadow Foreign Secretary, Douglas Alexander, have repeatedly voiced their support for a two-state solution and opposition to boycotts.
One expert suggested the motions had been proposed to spite the politicians and were indicative of a hard-left separation from policies being developed by Labour in Westminster.
"It's indicative of what's going on. There's a breakaway from Labour's mainstream policies. It's quite worrying," the insider said.
Unison's national delegate conference begins in Brighton on Tuesday, with Unite - Britain's biggest union - holding its policy conference in Liverpool from June 30.
Trade union members in Brighton will be asked to extend their boycott, divestment and sanctions campaigning. There will also be a series of attacks on former Israeli Prime Minister Ariel Sharon following his death earlier this year. One motion will criticise those who expressed admiration for him, and is expected to predict: "The continued onslaughts against the Palestinians will sooner or later be answered again with a massive struggle by the Palestinians".
Trade Union Friends of Israel director Stephen Scott called on Unison's national executive committee to reconsider its plans to oppose a motion backing a two-state solution.
"How can you oppose a policy that actively supports peace and reconciliation through the means of the global trade union movement?" he said.
Unite's conference later this month will go further in its attacks. One proposed motion reads: "Conference notes the continuing state-sponsored policy of ethnic cleansing and apartheid inside the West Bank, in Jerusalem and in Israel."
Another notes: "Palestinian children are arrested, tortured and killed on a regular basis, yet the world's power brokers choose to ignore international law and basic human rights when it comes to the Palestinians, choosing instead to support the colonisers of Israel."
Delegates in Liverpool will also be asked to blame Israel for the deteriorating situation in the Yarmouk refugee camp in Syria.
There is expected to be, however, at least one motion backing the work of both Israeli and Palestinian trade unions.