The Obama administration's plan to give US states more power to protect consumers from unfair banking practices would make it more difficult and costly for large lenders to operate across the country, a financial regulator has warned.

John Dugan, who oversees national banks as comptroller of the currency, told the Financial Times that the proposals to create a federal consumer protection agency and give states more leeway to crack down on unfair practices would have negative “ramifications for companies operating across state lines”.

Mr Dugan, who faces the loss of some of his powers if the plan is implemented, argued that repealing the 145-year-old system that gives federal banking rules precedence over state laws would confuse banks and discourage them from offering consumer products across the country.

“To have a single set of standards has been very beneficial to developing and innovating products,” Mr Dugan said, adding that he wanted to keep national banks “immune” from state regulation.

The remarks by the head of the Office of the Comptroller of the Currency, which is part of the Treasury, the department behind the proposed rules, shows the political high stakes surrounding the post-crisis regulatory framework.

Since the plan was announced by Tim Geithner, Treasury secretary, in June, Congress, regulators, banks and large companies such as General Electric have been trying to influence the final shape of any new laws.

Some lawmakers have opposed the administration's plans to give the Federal Reserve powers to police all financial groups whose failure could endanger the system, and banks have criticised the new consumer agency.

As part of a system introduced during the civil war, federal rules enforced by the OCC override state law. The administration plan, however, would enable the new consumer agency to draft minimum consumer protection standards, leaving states free to adopt more stringent rules.