A leading trade union is to cut its affiliation funds to Labour from £1.2 million to £150,000 in the wake of the row over party reforms.
The GMB said there will also be further reductions in spending on Labour Party campaigns and initiatives.
The decision by the 65-member executive follows plans by Labour leader Ed Miliband to give individual union members the choice of opting to join the party rather than being automatically affiliated.
There have been estimates that the change will cost Labour at least £9 million, a figure backed up by the GMB decision.
The union has affiliated 420,000 of its members to Labour, at £3 per member per year, but that figure will be cut to 50,000 from January.
The union said in a statement: "The GMB central executive council (CEC) has voted to reduce its current levels of affiliation to the Labour Party from 420,000 to 50,000 from 2014.
"This will reduce the union's basic affiliation fee to Labour party by £1.1 million per year.
"It is expected that there will further reductions in spending on Labour Party campaigns and initiatives.
"GMB CEC expressed considerable regret about the apparent lack of understanding the proposal mooted by Ed Miliband will have on the collective nature of trade union engagement with the Labour Party.
"A further source of considerable regret to the CEC is that the party that had been formed to represent the interest of working people in this country intends to end collective engagement of trade unions in the party they helped to form.
"The CEC also decided to scale down by one third the level of its national political fund."