The nation's biggest credit card companies are under increasing pressure to stop selling add-on credit card products to customers who don't really need them.

In a quarterly financial report released last week, American Express said it "currently believes" two of its subsidiaries could face penalties from the Consumer Financial Protection Bureau for using misleading advertising to sell credit card add-ons, like identity-fraud protection and credit-monitoring plans. The company has set money aside to refund customers, the report said.

On Monday, CFPB spokeswoman Moira Vahey said the disclosure by American Express does not necessarily mean the company will be penalized or refund customers' money. She said the bureau does not comment on pending investigations.

A spokeswoman from American Express said, "The discussions with regulators are confidential and we have not announced anything beyond what we said in the 10Q."

Bank of America also disclosed in its quarterly filing that it received queries from regulators regarding identity-theft products it offers cardholders. Discover Financial Services expects to face the CFPB regarding its sales of add-ons too, the Wall Street Journal reported.

The latest disclosures from some of the nation's biggest credit card companies reveal the teeth of the year-old government bureau. In July, the CFPB ordered Capital One Bank to refund customers $140 million for deceptive advertising of add-on credit card products.

Credit card add-ons like payment insurance, identity theft alerts or credit monitoring are lucrative up-sells for credit card companies, and mean hundreds of millions of dollars in revenue each year. Discover Financial reportedly made $300 million in 2009 on the sale of add-ons, according to a report from the Minnesota attorney general's office.

But some credit card experts said a crackdown on add-on products will only mean new customer fees, such as new costs to redeem rewards points.

"[Credit card companies] are not going to sit on the sidelines and take a punch to the bottom line without trying to offset revenue," said Curtis Arnold, founder of CardRatings.com, a credit card consumer education and comparison website.

Consumer advocates have long complained that these products mislead consumers, and rope them into fees they did not intend to sign up for and result in products with little meaningful value.

"[These add-on products] often have terms that make it sound like something you can't live without," said Linda Sherry, director of national priorities of Consumer Action, a consumer advocacy group. "Very few people understand that this [results in a recurring] fee and unless you're watching your account closely, it will continue to bill."

Several states have tried to take on credit card companies themselves. In April, Hawaii sued seven banks over deceptive marketing of payment protection services. West Virginia settled with Capital One for $13.5 million in January 2012, and Minnesota sued Discover at the end of 2010.

The bureau released a bulletin last month detailing its expectations surrounding advertising and marketing of add-on products, including clear terms and conditions, and forbidding credit card employee compensation from being tied to the sale of these products.

Since June 19, when the CFPB's new credit card database opened to the public, at least 100 new consumer complaints about credit card protection programs or company marketing have been logged. There have been more than 2,561 complaints logged since the database was made public in June.