Sienna Miller dons a green mask to encourage people to become "part of the world's biggest bank job" in a new ad.
The Factory Girl and Alfie star helped launch a digital advertising campaign backing a proposed tax on banks which campaigners said could help millions of poorer people.
The Robin Hood Tax campaign is calling on political leaders to support a global tax on banks to help repair damage caused by the global economic crisis.
The proposed tax would only be levied on transactions between financial institutions, not on banks' transactions with their high-street customers.
While different rates of tax would apply to different types of transaction, they would start at five cent for every €1,000 traded -- an average of 0.05pc.
Miller said: "A tiny 0.05pc tax on bankers could raise billions for public services and tackle poverty and climate change at home and abroad -- small change for the banks can mean big changes for the world."
The campaign was launched with a short film by Love Actually director Richard Curtis, starring Bill Nighy in the role of a banker reluctantly accepting the merits of the tax.