Lazard Ltd and Morgan Stanley risk losing up to $33 million in advisory fees if the U.S. government is successful in stopping Anheuser-Busch InBev SA from buying the half of Mexican brewer Grupo Modelo that it does not already own.
On Thursday, the U.S. Justice Department filed a lawsuit seeking to stop the $20.
The deal, which was announced in June, would have been the third biggest M&A transaction in 2012, according to Thomson Reuters data.
If the deal falls through, Lazard - financial adviser to AB InBev on the transaction - would likely lose $11 million to $15 million in fees, while Modelo's financial adviser Morgan Stanley could lose $14 million to $18 million, according to estimates from Freeman & Co LLC.
The potential loss of fees would come at a time when investment banks are already feeling the pinch from anemic mergers and acquisitions activity.
Deal volumes are down more than 8 percent globally in 2012 from the previous year, and down 17 percent compared to the levels of 2007, according to Thomson Reuters data. Deals that are still taking place are smaller, with average deal size down 24 percent last year compared to 2007.
AB InBev said in a statement that it intends to "vigorously contest" the U.S. decision in federal court, adding that it was "inconsistent with the law, the facts and the reality of the market place."
(Reporting By Jessica Toonkel, Editing by Soyoung Kim, Bernard Orr)