Senate investigators estimate that Americans who hide assets in offshore bank accounts are failing to pay about $100 billion a year in taxes. In good times, that’s grossly unfair and bad for the country. In times like these, it should be intolerable. The government not only needs the money, but closing down such tax scams is essential for President Obama’s rescue effort to retain public support and credibility.

Some of the banks at the center of the global financial meltdown are prominent purveyors of evasion services. UBS of Switzerland has acknowledged that as of Sept. 30, it held about 47,000 secret accounts for Americans. It has refused to disclose the names of all but a tiny number of the account holders, arguing that it would be a breach of Swiss law. But last month  after UBS got caught soliciting business in the United States  it admitted to breaking federal law by helping Americans hide assets, and the bank agreed to pay $780 million in fines and restitution.

The United States Treasury isn’t the only one being shorted. The Tax Justice Network, a research and advocacy organization, estimates $11.5 trillion in assets from around the world are hidden in offshore havens.

The United States also isn’t the only country running out of patience. In February, European leaders forged an unusually tough and united call to put the problem of “uncooperative jurisdictions” near the top of the agenda for the April summit of leading economies in London. (Finance ministers will discuss the issue at a preparatory meeting in London this weekend.)