The 'Mr 10%' campaign picks up on comments made by Conservative shadow health secretary Andrew Lansley which indicated his party would cut public spending by 10% across most government departments.
It is designed to drive Labour supporters to a new section of Labour's website where they can sign a petition calling on David Cameron to explain where his cuts will fall.
Online mechanics include an animated widget available from Labour.org.uk which supporters can share through Facebook or their own websites, banner ads, paid-for search marketing, and emails from home secretary Alan Johnson.
Thousands of leaflets are being handed out by party activists across the country and material tailored by MPs to their constituencies.
Greg Jackson, chief executive at Tangent One, said: "The 'Mr 10%' campaign, with its integrated online and offline components, has been turned around in less than a week."