Federal Reserve Chairman Ben Bernanke says the central bank is looking into Goldman Sachs and other Wall Street firms' use of a sophisticated investment instrument to make bets that Greece will default on its debt. Bernanke says the Fed is looking into companies' use of credit default swaps, a form of insurance against bond defaults. Bernanke made the comments at the start of a Senate Banking Committee hearing. The panel's chairman, Sen. Christopher Dodd, says he is troubled that this practice could worsen Greece's debt crisis. On Wednesday, some 50,000 Greek workers took to the streets and a few protesters threw rocks and red paint in clashes with police during the widest strike yet against the government's austerity plan aimed at easing the country's debt crisis. Greece is considering tough austerity measures to ward off a financial crisis that has undermined the euro currency used by Greece and 15 other European nations. The country's troubles have raised fears that financial market contagion will spread to other weak eurozone economies such as Portugal, Spain and Italy. Officials from the EU and International Monetary Fund are in Athens to inspect public finances, ahead of a March 16 deadline to show signs of fiscal improvement or face additional austerity measures. Greece has promised the EU it will reduce its budget deficit from 12.7% of gross domestic product to 8.7% this year. The country's woes have caused the euro to sink against the dollar and hiked the country's borrowing costs.