But she emphasized that the audit focused only on billing mistakes.

Ogilvy has said the charges are related to billing mistakes for which it has already compensated the government.

The 407 ETR Concession Company, which was given a 99-year lease to operate the expressway in 1999, acknowledges that it makes billing mistakes.

We have noticed these little billing mistakes for several years.

Like the indictments against two former employees last month, it is related to billing mistakes for which Ogilvy compensated the government in a settlement announced two years ago.

AT&T and Verizon both lost a custom in me with all their billing mistakes and hostile customer service when it was a clear issue on their side.

Ms. Strebel's lawyers say she made an innocent billing mistake, and they say her indictment and trial are politically motivated.

He said the group's members faced a raft of different requirements from Medicaid, Medicare and numerous private insurance companies, and as a result made billing mistakes that were wrongly criminalized.

"We recognized our responsibility for our billing mistakes," Ogilvy said in a statement last week, "and cooperated fully with the government to resolve them."

Behind the scenes, both companies have begun improving their vast credit-card transaction networks to eliminate the billing mistakes responsible for many of those checkout-counter blunders.