Unions opposed to Ed Miliband's planned reforms of Labour fear the changes will relegate them to “placard carriers and cheque writers”, sources said today.
Debate is still raging over the GMB's decision to cut its affiliation funds from £1.2 million to £150,000 in the wake of Mr Miliband's move.
He wants union members to opt in to joining Labour rather than being automatically affiliated, a decision which could cost the party millions of pounds.
The Labour leader is due to meet GMB general secretary Paul Kenny later today.
Union officials believe the reform will weaken the historic link between Labour and the unions, and even threatens to sever it altogether.
“Trade unions are collective bodies and affiliate to Labour as the best way of campaigning for social change and justice,” said a union source.
“Each year, union members support the principle of affiliating to Labour and spending money on the basis of a collective structure.
“Under the changes, things are transferred to individual members. The vision seems to be: ditch the affiliation but don't ditch the unions altogether.
“Our role would be one of placard carriers and cheque writers.”
Labour said its biggest financial contribution comes from small donations and members, adding that the affiliation fund issue was a matter for the GMB.