Big Wall Street banks are pushing back at an attempt by the AFL-CIO to ban an executive perk that rewards executives who leave their posts for jobs in the government, the New York Times DealBook blog reported yesterday. So-called government service golden parachutes allow bank executives heading for top government jobs to be paid their unvested stock and equity awards when they leave, rather than forfeit them as they normally would at resignation. The labor organization said yesterday that it was seeking to ban the practice at Citigroup, Goldman Sachs, JPMorgan Chase, Morgan Stanley, Lazard and Bank of America.