Sussan Ley’s shadow cabinet has formally resolved to oppose Labor’s new tax increase on superannuation balances above $3 million, labelling it “grossly unfair on every single count”.

But the action, which confirms the Coalition’s long-held hostility towards the tax that was first proposed two years ago, will have no impact on its passage. Labor and the Greens are poised to pass the legislation when parliament resumes in late July.

The government could not secure the passage of the legislation last term because Senate crossbenchers, including David Pocock, Jacqui Lambie and Tammy Tyrrell, opposed it on the basis that it taxed unrealised gains and the $3 million balance threshold was not indexed.

But now Labor and the Greens have the requisite numbers between them in the Senate to pass bills.

The Green have no qualms about taxing unrealised gains but want the $3 million reduced to $2 million and indexed. The government has said it will not cede to this demand and believes the Greens will fold.

After the shadow cabinet meeting, shadow treasurer Ted O’Brien said the Coalition would fight the tax “every step of the way”.

“It defies everything we believe in as a Coalition,” he said, in that it was a tax increase and it taxed unrealised capital gains.