“Tax Wall Street,” read a sim­ple, home­made plac­ard high above the crowd of thou­sands of mem­bers of unions, com­mu­ni­ty groups and Occu­py activists protest­ing out­side the mid-Octo­ber con­ven­tion of bankers and futures traders in down­town Chica­go. Cur­tis Smith, pres­i­dent of the local affil­i­ate of Nation­al People’s Action, a net­work of com­mu­ni­ty orga­ni­za­tions focused on the mort­gage cri­sis and finan­cial indus­try reform, seized a micro­phone to detail the demand.

The tax would make Wall Street better serve the Main Street economy, and it would generate tens -- even several hundreds -- of billions of dollars annually in much-needed revenue for worthy projects.

Among oth­er mea­sures, Smith pro­posed a tax on finan­cial trans­ac­tions, includ­ing the sale of stock, bonds and deriv­a­tives. The tax would make Wall Street bet­ter serve the Main Street econ­o­my, and it would gen­er­ate tens – even sev­er­al hun­dreds – of bil­lions of dol­lars annu­al­ly in much-need­ed rev­enue for wor­thy projects. Gov­ern­ments would col­lect the tax on finan­cial trans­ac­tions most prone to harm­ful spec­u­la­tion, and wealthy indi­vid­u­als and finan­cial insti­tu­tions would main­ly pay. That’s why NPA and British cam­paign­ers call it the ​“Robin Hood tax.”

In the weeks before the Chica­go protests, the Euro­pean Com­mis­sion had pro­posed a finan­cial trans­ac­tion tax for Europe by 2014 – revers­ing its ear­li­er rejec­tion of an FTT. Con­ser­v­a­tive lead­ers of both France and Ger­many – Nico­las Sarkozy and Angela Merkel – vowed to press adop­tion of the tax at the G20 lead­ers meet­ing in France in ear­ly Novem­ber, despite oppo­si­tion from the con­ser­v­a­tive British gov­ern­ment and the Oba­ma admin­is­tra­tion. On Novem­ber 3, inter­na­tion­al union del­e­ga­tions demon­strat­ed for an FTT out­side the G20 conference.

In Wash­ing­ton on the same day, Nation­al Nurs­es Unit­ed protest­ed with oth­er unions and allies, urg­ing Con­gress to ​“Heal America/​Tax Wall Street,” and labor-com­mu­ni­ty ral­lies around the coun­try urged polit­i­cal lead­ers to enact the tax. And in Con­gress, one day ear­li­er, Sen. Tom Harkin (D‑Iowa) and Rep. Peter DeFazio (D‑Ore.) re-intro­duced their pro­pos­al for a very mod­est FTT.

The idea of impos­ing a very small tax on some sales of finan­cial prod­ucts is not new; British econ­o­mist John May­nard Keynes pro­posed a stock spec­u­la­tion tax in the 1930s. In recent years, the FTT has picked up sup­port from some promi­nent busi­ness lead­ers (includ­ing War­ren Buf­fett and Bill Gates) and many econ­o­mists, from Nobel Prize win­ners Joseph Stiglitz and Paul Krug­man to the 1,000 econ­o­mists from 53 nations who signed a let­ter last April say­ing an FTT was ​“tech­ni­cal­ly fea­si­ble” and ​“moral­ly right.” The Inter­na­tion­al Mon­e­tary Fund iden­ti­fies 24 coun­tries that cur­rent­ly have an FTT, most promi­nent­ly a long-stand­ing tax on stock sales in Britain, home to one of the world’s largest finan­cial markets.

FTT advo­cates think the finan­cial trad­ing busi­ness has grown too big, too spec­u­la­tive and too par­a­sit­i­cal­ly destruc­tive of the real econ­o­my. Cen­ter for Eco­nom­ic and Pol­i­cy Research (CEPR) co-direc­tor Dean Bak­er, a pio­neer FTT pro­po­nent, notes that invest­ment bank­ing and trad­ing quin­tu­pled as a share of the U.S. econ­o­my from the 1970s to the last decade. Bank­ing is like truck­ing, Bak­er says – an inter­me­di­ate good. An effi­cient econ­o­my min­i­mizes the truck­ing or finan­cial activ­i­ty required to pro­duce goods and services.

Crit­ics say an FTT would dis­tort finan­cial mar­kets, would be hard to col­lect and, unless enact­ed glob­al­ly, would dri­ve busi­ness out of taxed coun­tries. Ide­al­ly, all coun­tries would coop­er­ate, but coun­tries can act indi­vid­u­al­ly. London’s stock mar­ket has man­aged to pay its tax and thrive. Experts have also devel­oped sophis­ti­cat­ed designs to min­i­mize harm­ful distortions.

A broad-based FTT (0.5 per­cent on stocks and options, or about 50 cents per $100 trade) could yield rough­ly $170 bil­lion in fed­er­al rev­enue annu­al­ly, accord­ing to a study by CEPR and the Uni­ver­si­ty of Mass­a­chu­setts. Oxfam, a lead­ing advo­cate, says the mon­ey should be used for inter­na­tion­al devel­op­ment. Oth­er pro­po­nents sug­gest deficit reduc­tion, job cre­ation, eco­nom­ic sta­bi­liza­tion, glob­al warm­ing pre­ven­tion and oth­er causes.

Repub­li­cans in this Con­gress sure­ly will block any FTT pro­pos­al, even if Pres­i­dent Oba­ma revers­es his cur­rent posi­tion to sup­port the tax (as he once did), but Euro­pean momen­tum may even­tu­al­ly push the Unit­ed States to act. ​“At a min­i­mum it appears a group of G20 coun­tries are going to move for­ward with finan­cial trans­ac­tion tax­es, along with the Euro­pean Com­mis­sion,” says AFL-CIO Pol­i­cy Direc­tor Damon Sil­vers. ​“The U.S. should be part of this glob­al effort so that Pres­i­dent Oba­ma is clear­ly with the glob­al 99% and not the Wall Street 1%.”