Massachusetts' top financial regulator has asked securities dealers that issue credit cards, including American Express Co. and Charles Schwab Corp., for information about rate and fee increases imposed ahead of a new federal law.

Commonwealth Secretary William Galvin sent letters to seven companies that issue credit cards to their customers themselves or through affiliated banks, seeking details on changes in credit card terms since May, when President Obama signed the Credit Card Accountability, Responsibility and Disclosure Act.

"When the credit cards and the abusive new practices being put in place are tied to securities broker-dealers, there is a question whether they are acting under the high standards of commercial honor and the just and equitable principles of trade," Galvin said Thursday.

Letters of inquiry also were sent to Morgan Stanley, Bank of America Corp., Citigroup Inc., Royal Bank of Scotland's Citizens Financial Group Inc. and Fidelity Investments. The companies were given until Jan. 26 to respond with the information sought.

Bank of America, Amex, Schwab, Citizens and Fidelity did not immediately return messages seeking comment.

Morgan Stanley spokesman Jim Wiggins had no comment, and Citigroup spokesman Samuel Wang declined to comment.

The law, which is to take full effect by August, includes limits on rate increases and requires that payments above the monthly minimum be applied first to higher-rate balances.

Card-issuing banks, including Citigroup, JPMorgan Chase & Co. and Wells Fargo & Co., have raised rates and fees and switched their interest rate models from fixed to variable, arguing that the new rules would make it more difficult to price for risk.

An attempt to speed up enforcement of the rules by lawmakers including Senate Banking Committee Chairman Christopher Dodd, D-Conn., stalled amid Republican opposition.

Lenders have sought to circumvent the law "by charging what seem to be onerous and unnecessary fees such as annual fees, inactivity fees and transfer fees before the legislation takes full effect," Galvin's office said in a Jan. 11 letter to Bank of America General Counsel Edward O'Keefe.

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