WASHINGTON (AP) – The Senate acted Friday to impose more oversight on the biggest credit-rating agencies, criticized by some lawmakers as unfairly dominating the field and hindering competition.

The three powerful Wall Street agencies – Moody’s Investors Service, Standard & Poor’s and Fitch Ratings – largely police themselves. An array of critics have pressed for legislation that would give the Securities and Exchange Commission expanded oversight over the credit raters.

The agencies issue grades of creditworthiness on companies with publicly held securities. Their ratings are closely watched by markets and can determine whether banks and other financial institutions invest in a company.

The bill, passed by voice vote, seeks to increase competitiveness in credit rating by establishing a registration process for other companies that want to gain recognition as nationally recognized statistical rating organizations.

It would allow the SEC to suspend or revoke an agency’s registration for the protection of investors and the public interest if it detects misconduct at an agency. It also calls for more disclosure of potential conflicts of interest.

Some lawmakers have described the bill as the final reform needed after a wave of corporate accounting scandals.

The credit rating agencies came under criticism for failing to detect and warn investors of the startling accounting failures at large companies that eventually collapsed. They maintained high ratings for Enron Corp., for example, until four days before its bankruptcy filing, even as its stock plummeted.

The SEC had no immediate comment.