Labour is set to reignite a major row over how it selects its party leader, with a vote expected on a return to the system that hands MPs more power.

Keir Starmer outlined plans for a return of an electoral college system to his shadow cabinet on Tuesday. The plans have been fiercely opposed by trade unions including Unite and TSSA, which have said they will fight them on the conference floor.

Labour also plans to change its policymaking process, which could deny members a chance to vote on the plans at party conference. Instead, Starmer told his shadow cabinet the movement would have input to the policymaking process but that would not involve “an endless series of motions at party conference”.

On Friday, members of the party’s ruling national executive committee are to consider returning to the system that pre-dated Jeremy Corbyn‘s election as Labour leader, known as the electoral college.

The change, which would be presented at the party’s conference this weekend, is likely to infuriate the party’s left because it would diminish the power of party members.

The move would be a return to Labour’s old electoral college, where MPs, party members and trade unions each had a third of the votes. That system was abolished by Ed Miliband in 2014, giving each member of the party and its affiliates one vote on any candidate on the ballot paper. Candidates must acquire support of 10% of MPs, plus constituency parties and trade unions, to get on the ballot.

Starmer is to meet trade union leaders on Wednesday to brief them on the changes, which will also cover the levers for deselecting MPs.

He told the shadow cabinet: “Our rules as they are right now, focus us inwards to spend too much time talking to and about ourselves and they weaken the link with our unions. I hope Tulo [the Trade Union and Labour Party Liaison Organisation] will support me, I believe these changes are good for their members and they strengthen our link. I know that this is difficult – change always is – but I think these changes are vital for our party’s future.”

Unite’s new general secretary, Sharon Graham, said the plan was “deeply disappointing” and urged MPs to oppose it. “Unite believes in democracy and this move to reduce the entire membership to one-third of the vote while inflating the votes of MPs to one-third is unfair, undemocratic and a backwards step for our party.”

The TSSA’s general secretary, Manuel Cortes, called the move “gerrymandering” and wrote to Starmer to express his anger. He said it was “the sort of thing associated with Victorian Tories” and that the “union will have no hesitation in voting against this gerrymandering if this proposal makes it anywhere near conference floor”.

A Labour source said Starmer would aim to convince the unions that they would have more power under a return to the old system, pointing to the election of Miliband in 2010 when members and MPs had backed his brother, David, but the union vote had sealed the younger Miliband’s election.