Proponents of arbitration, who say it provides an efficient alternative to courts, view the Consumer Financial Protection Bureau as among its biggest threats. They say a new rule proposed by the consumer agency, which would prevent financial services companies from including class-action bans in consumer contracts, could in effect kill arbitration altogether.

On Wednesday, the Justice Department issued a proposal to protect military service members from arbitration requirements. Earlier this month, Senator Al Franken, Democrat of Minnesota and a longtime opponent of arbitration, renewed his push for Congress to pass a bill he introduced this year that would prevent companies from requiring employees to go to arbitration.

Several Democrats are expected to introduce bills intended to more widely curtail the use of arbitration clauses, according to the people who knew of the strategy. But with Congress deeply divided, some Democrats are calling on President Obama to use his executive authority to prevent federal contractors from including arbitration clauses in their contracts with customers and employees.

San Francisco’s city attorney, Dennis Herrera, sued American Express this month over what he claimed were “illegal and anti-competitive rules, policies and practices.” The lawsuit, filed in Superior Court, will probably help small businesses whose contracts with the credit card company prevented them from filing a class-action lawsuit.

Marina H. Norville, a spokeswoman for American Express, said, “We don’t believe the suit has merit,” adding that the company planned to “vigorously” defend itself against it.

In Chicago, Alderman Edward M. Burke said he planned to introduce a bill this week that would prevent the city from doing business with companies that push employees and customers out of court. “It’s a way to get at a practice that is destroying a core American principle,” he said in an interview.