Govt smoking tax to raise $28.2bn

Labor will have to find an extra $20 billion in funding after a leaked federal budget document showed a shortfall in the opposition's expected revenue from taxing smokers.

In a document obtained by the Nine Network, Treasury forecasts the tobacco excise will raise $28.2 billion over 10 years.

That's $19.8 billion less than Labor had predicted over the decade, leaving it short on funding for its spending promises - including fully funding the Gonski school model.

Labor frontbencher Anthony Albanese dismissed the leak, saying it didn't show what the government's policy on the tobacco tax actually was.

Often what the government spins was different to reality, he said, and Labor would wait to see the detail.

"I've learnt not to trust government spin, let alone a drop," he told Sky News.