The Deputy Prime Minister Nick Clegg, writing in Sunday's Observer, has fiercely rebuked Conservative Eurosceptics.
Clegg has staked out his position opposing the Conservative right by insisting that the coalition will not be taking back powers from Brussels. He warned it would be "economic suicide" for Britain to "retreat to the margins" of Europe.
The strident article raises the prospect that Britain's relationship with Europe could prove to be a dangerous sticking point within the coalition, with most Lib Dems being pro-European and the right-wing of the Conservative Party being historically Europsceptic.
Clegg fears that this is entirely the wrong time to be debating EU membership. When we should be focused on economic growth, he explains, "tampering with the EU's founding texts" would open a "Pandora's Box". Europe, instead of strengthening its economic position in the wake of the Eurozone crisis would be left "paralysed by ideological battles, institutional navel-gazing and special demands from every member state".
Clegg's forthright article comes as Mr Cameron has faced a fraught week in parliament with rebellious Conservative MPs over Europe. 81 of them defied a three-line whip last week last week in order to support a referendum on Britain's membership of the European Union.