If, as reported, Interpublic does reveal a higher figure, it will be the second time it has been upped since the company revealed $68.5m in improperly booked expenses in August.
The company, whose other agencies include Lowe & Partners and Initiative Media, is due to publish its results on Wednesday. According to a report in the Wall Street Journal, the amount of the discrepancy could be more than $120m although the amount in excess "could be small".
After revealing the initial mistake of $68.5m, Interpublic has launched an internal investigation, which is thought to have turned up larger errors than initially thought.
The fallout has already seen Sal LaGreca, chief financial officer of McCann-Erickson, leave the company, and Interpublic vice-chairman David Bell give up key responsibilities. Last week, the company named Frank Borelli to the position of presiding director, charged with ensuring that the board and senior management communicate more effectively.
McCann-Erickson Europe is at the centre of the scandal. The problems have arisen over charges made to clients operating in more than one market, which saw different McCann offices booking the same revenue. Although clients were not overcharged, the mistake meant that revenue was inflated over several years.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the .