Chris Leslie, the shadow chief secretary to the Treasury, will warn voters that "lower priorities will get less money".
And he will reiterate his party's stance that it will be unable to reverse cuts introduced by the Tory-Liberal Democrat Coalition.
In a speech, he will say: "I'm not heading into this expecting popularity. Quite the opposite.
"We won't be able to undo the cuts that the have been felt in recent years, and I know this will be disappointing for many people."
He will also add: "A more limited pot of money will have to be spent on a smaller number of priorities. Lower priorities will get less."
Labour is currently carrying out a "zero-based" review of every pound of government spending, and the party has claimed it would cut the deficit and return the budget to a surplus.
But Mr Leslie will also say that Labour's long-awaited policy review would not be about spending commitments - a revelation the Conservatives will seize on to say the party cannot be trusted on the economy.
After the last general election a number of senior Liberal Democrats openly said that they expected to be unpopular in government.
Chris Huhne, the then energy secretary, famously said in August, 2010: "Frankly in a year's time, I think both the Conservatives and Liberal Democrats are going to be pretty unpopular because we will have to take very, very tough decisions because of the legacy that Labour has left us in terms of this massive deficit."