Bill Shorten dismissed the advice of a majority of his shadow cabinet when he announced Labor would only support an increase to the Medicare levy for people earning more than $87,000 a year.

Fairfax Media has confirmed with three shadow cabinet ministers that during a shadow cabinet meeting a day before the opposition leader's budget reply speech, a majority of Labor MPs argued for the party to back the Turnbull government's across-the-board 0.5 per cent rise in the Medicare levy.

The leaking of details from Mr Shorten's shadow cabinet is rare, underscores the disquiet within opposition ranks, and will likely be seized on by the Turnbull government.

Nine MPs addressed the Wednesday meeting of the shadow cabinet about the Turnbull government's policy, which is designed to raise $7.8 billion over two years from July 2019 to help fund the National Disability Insurance Scheme.