When federal regulators told Congress in April that they lacked basic plans for the oversight of consulting firms that advise big banks, one lawmaker had blunt advice: start adopting guidelines “this afternoon.”

With changes yet to materialize, the lawmaker, Senator Sherrod Brown, plans to ratchet up the pressure on Friday in a letter to the nation’s top banking regulators.

In the letter — a draft of which was reviewed by The New York Times — Mr. Brown will urge the Federal Reserve and the Office of the Comptroller of the Currency to keep a closer watch on the multibillion-dollar consulting industry, which has become something of a shadow regulatory force on Wall Street.