Ed Balls has issued a fresh appeal to Business Secretary Vince Cable to work with Labour on a Plan B for the economy as he seeks to exploit coalition tensions.
The shadow chancellor said he wanted to join forces with "sensible people in the Government" - singling out the senior Liberal Democrat and giving renewed backing to the "mansion tax" championed by Mr Cable.
His article in the Sunday Mirror came a day after opposition leader Ed Miliband said he was in regular text message contact with the Business Secretary and was "open for business" for joint working in the future.
Deputy Prime Minister Nick Clegg has dismissed claims that his party colleague, tipped by some to lead the party into the 2015 election, was being courted by Labour as "ridiculous" and "schoolboy politics".
But Mr Balls used the article to directly target Mr Cable . The pair are both due to be guests on BBC1's Andrew Marr Show.
He wrote: "No matter how bad things get, David Cameron, George Osborne and Nick Clegg are desperate to cling on to their failing economic plan - putting their political pride above the long-term interests of the country. But the country cannot afford to wait until the next election before we get a change of course. Because the longer ministers refuse to act, the more long-term damage will be done to our economy.
"That's why I want to work with other parties - including sensible people in the Government - on a new economic plan. In his heart of hearts... Vince Cable must know that Plan A is not working. After all, before the last election, he warned - with Labour - that David Cameron and George Osborne's policies would backfire. And sadly our warnings came true. So let's work together on new ideas to create jobs and build our way out of recession."
Mr Balls' latest intervention, citing new infrastructure projects, a VAT cut on home improvements and the mansion tax, came as one of the two new Tory ministers moved into Mr Cable's department in Prime Minister David Cameron's reshuffle called for an end to the "politics of envy" that sought to tax wealth.
In what will be seen as a shot across the bows of the Business Secretary, Michael Fallon said it was vital to "salute" wealth creation "and stop thinking of new ways to tax it". And he told the Sunday Telegraph that he would champion the scrapping of up to 3,000 regulations, the complete sell-off of the Royal Mail and moves to make it easier to sack underperforming staff.
The installation of Mr Fallon and close George Osborne ally Matthew Hancock under Mr Cable was regarded as a bid to restrain the senior Lib Dem, regarded by some Tories as being anti-business. Mr Fallon denied that was the case, telling the Sunday Telegraph: "I'm not there to keep an eye on Vince Cable, I'm there to keep both eyes on growth."