Labour's shadow cabinet needs to "play as a team" and should be honest with the public about spending cuts, according to Lord Mandelson.
The former Business Secretary and New Labour co-architect said there was "no point" leaving Ed Miliband and Ed Balls to make the statements.
"The shadow cabinet as a whole has to play as a team on this," the former European Commissioner for Trade told the BBC's Andrew Marr Programme.
But he said Labour had "put the deficit ball in the back of the net" in recent weeks.
"To keep it there, each member of the shadow cabinet has got to be honest with the public," he added.
"They've got to set out what this means for their own departmental budgets and demonstrate to the public that they mean it."
The comments come after Balls, the Shadow Chancellor, wrote to Labour's front bench team to warn them that they face cuts in their departmental budgets until the deficit has gone.
Prime Minister David Cameron says Labour's plans are a "massive gamble" that will leave Britain vulnerable to another financial crash.
"At the height of the so-called boom years, far from running a surplus, Britain was running the biggest structural deficit in the G7. Then, in 2008, when the economic storms hit, we were completely exposed," Cameron said.
"Our plan is about making sure that doesn't happen again. It's about saying that by 2018 we will be putting money aside so that if any crash or shock happens to our economy, we will be better prepared.
"And frankly, if we are not going to start putting money aside after seven years of continued economic growth, when will we be?"
He added: "Miliband spoke about the deficit - and wrapped it all up in a lot of jargon.
"He claimed he would run 'a surplus on the current budget' and attacked our plans to 'balance the overall budget'. I want to peel back the jargon and tell you what this actually means.
"Miliband is saying he will only balance part of the government's budget, not the whole thing like we plan.
"And let's be clear what that means: Miliband would never clear the overall, headline budget deficit.
"He would run a budget deficit, permanently adding to debt indefinitely. Every year. Forever."