The Scottish Finance Secretary is calling on the Chancellor to rethink "disastrous" benefits changes in next week's Budget.
John Swinney has written to George Osborne, challenging him to withdraw changes to housing benefit for those deemed to have spare rooms - the so-called "bedroom tax".
Mr Swinney criticised the Chancellor for choosing "austerity over investment in jobs and growth" as he demanded he provide more cash for capital investment.
He is also urging the UK Government to act on the distribution of European structural funds after it was estimated the amount of cash Scotland receives as part of this scheme could fall by about a third.
The Finance Secretary also made fresh calls for responsibility for air passenger duty to be devolved to Scotland and for the Conservative-Liberal Democrat coalition at Westminster to do more to improve access to finance for small and medium-sized businesses.
His plea comes in advance on the UK Budget on Wednesday.
Mr Swinney said: "Since 2010 the UK Government's fiscal policy has been premised on the need to maintain market confidence and the UK's AAA credit rating."
But he added: "The Chancellor has chosen austerity over investment in growth and jobs, and the cost has been the continuing deterioration in the public finances, prolonged recession and the downgrade of the UK's credit rating."
The Finance Secretary said the cost of this was "increasingly borne by the most vulnerable in our society" along with public services, which are now "urgently seeking to mitigate the worst impacts of the UK's disastrous welfare reform programme".
In his letter to the Chancellor, he said he was "particularly concerned" about the introduction of the under-occupancy penalty for housing benefit, saying this would affect more than 100,000 in Scotland.
