NEW YORK The companies that determine Americans’ credit scores are about to come under government oversight for the first time.

The Consumer Financial Protection Bureau said Monday that it will start supervising the 30 largest firms that make up 94 percent of the industry. That includes the three big credit-reporting firms: Equifax Inc., Experian and TransUnion.

In remarks prepared for a speech Monday, Richard Cordray, the government agency’s director, said that scorekeeping by credit bureaus plays such a large role in Americans’ financial lives, it requires scrutiny.

The bureau said its oversight may include on-site examinations and that it may require credit bureaus to file reports.

Cordray said the agency’s oversight will extend to niche companies that “focus on payday loans or checking accounts, as well as resellers of credit reports and those that analyze credit report information.”

The announcement wasn’t a total surprise, said Jon Ulzheimer, president of consumer education at SmartCredit.com and a former Equifax employee. He said the consumer bureau had hinted earlier this year that it was considering supervising the industry.

To Ulzheimer, the move implies that the bureau will soon clarify what the Fair Credit Reporting Act requires of credit bureaus, a constant source of debate in the consumer credit world. When a person challenges what’s in their credit report, the Fair Credit Reporting Act requires the bureaus to investigate.

“But what exactly constitutes a reasonable investigation?” Ulzheimer asked. “The act doesn’t say.”

Each of the three biggest credit-reporting agencies maintains files on more than 200 million Americans. These reports are filled with details on an individual’s payment history with credit cards, mortgages, auto loans and other borrowing, applications for credit, medical account information and other financial details. Past behavior, like late payments or carrying high balances on credit cards, is used to determine credit scores.

Lenders, like banks or auto finance companies, use credit scores to measure eligibility for mortgages, credit cards and a wide variety of other consumer loans. Low scores based on missed or late payments, for instance, can mean higher interest rates or rejected applications.

There have been thousands of complaints about the bureaus by consumers who claim they are unsuccessful getting credit-reporting agencies to correct inaccurate information contained within credit reports.

The protection bureau will start regulating the industry after the new rule takes effect on Sept. 30.