The story about the latest money-making efforts of the Wall Street banks should not be surprising. But it has a feel of adding insult to injury.

Over the past weeks and months, financial reporting has described corporate “inversions” in which a U.S.-based company buys a foreign owned company and then uses tax law and legal maneuvers to cut its tax bill by claiming to be headquartered in the other country, but without changing anything about its U.S. operations.

Several Fortune 500 companies have gone through these “inversions” as a way to save millions on their tax bill to Uncle Sam. By some estimates, these corporate inversions will cost U.S. taxpayers about $20 billion over the next decade. And for every dollar of lost tax revenue to the U.S. Treasury, other taxpayers are left to pick up the slack, paying more in taxes to replace what was lost to inversions.

Last week, it was reported that the big Wall Street banks were making millions of dollars guiding corporations through inversion deals. Not only are the Wall Street banks being paid to help companies do inversions, they are actively marketing inversion opportunities to clients, looking for the multimillion-dollar fees.

Already, there is growing outrage over the companies doing inversions. President Barack Obama has called them “corporate deserters” and a few members of Congress are working on legislation to stop the practice or at least make it less attractive.

For the Wall Street banks, especially those who received billions of dollars of taxpayers money as part of the federal bailouts during the financial crisis, this is not good public relations.

The biggest Wall Street banks, including Goldman Sachs and JPMorgan Chase, have been trying to polish their public image with philanthropy and keeping a low profile. Lloyd Blankfeif, CEO of Goldman Sachs is saying he’s worried about income inequality. He’s also said, “Investing in America still produces the best return.”

Then we learn that Goldman Sachs made about $203 million, since 2011, advising companies on how to cut their U.S. tax bill with the inversion loophole.

The big banks say that if they turn down inversion business for moral reasons, other banks will just get the fee income. The bankers and corporate executives at the center of inversions say that cutting U.S. corporate tax rates, which are now higher than any other country’s tax rates, is the best way to stop inversions.

That might be true. But Congress should make clear it plans to pass legislation that not only stops inversion-based tax dodges, but is also retroactive — to stop a mad dash of corporate deserters from trying to do deals before the law is changed.