The push for a so-called “Robin Hood tax” on stock trading and other securities transactions received an extra jolt this week, thanks to some celebrity power.

Actor Mark Ruffalo of the summer blockbuster “The Avengers” joined musicians Chris Martin of the band Coldplay and Tom Morello of Rage Against the Machine to promote the campaign on Tuesday.

Other prominent backers include Bishop Desmond Tutu, the South African anti-apartheid leader, and economist Jeffrey Sachs. Not long ago, the campaign was mostly supported in the U.S. by labor groups like National Nurses United and the Massachusetts Nurses Association, although it received celebrity support in the United Kingdom (see Nurses Urge Congress to Tax Financial Transactions and "Robin Hood" Tax Targets Bank Transactions). Now, according to the campaign, supporters include former executives from Goldman Sachs and JPMorgan Chase.

On Tuesday, they brought their message to the doors of JPMorgan Chase, holding rallies outside Chase bank branches in 16 cities, including Boston, Chicago, Los Angeles and Washington. The demonstrations were timed to coincide with JPMorgan Chase CEO Jamie Dimon’s testimony before the House Financial Services Committee on the bank’s recent multibillion-dollar trading loss.

The Robin Hood Tax promoted by the campaign would impose a sales tax of less than half of 1 percent—or 50 cents per $100 on trading in stocks, and even smaller assessments on bonds, derivatives and currencies, potentially raising billions of dollars in the U.S. For more information, visit

The chances of Congress passing such a tax are virtually zero. When Dimon testified before the Senate Banking Committee last week, a number of lawmakers appeared to bend over backwards to show the powerful banker they were on his side. The financial industry is one of the largest contributors to political campaigns, and its lobbyists managed to beat back many of the more far-reaching proposals for the Dodd-Frank financial reform law two years ago and weaken the regulations that the Securities and Exchange Commission has needed to spell out to carry out the law.

But proponents of a tax on financial transactions argue that the money would help close the gap on the devastating budget deficits that have forced local and state governments around the country to reduce services and lay off workers.