The US Securities and Ex-change Commission passed rules on Thursday to tighten supervision of credit ratings agencies following a torrent of criticism over their role in the financial crisis.

Credit ratings agencies, which are usually paid by the issuers they rate, came under fire during the crisis because they gave top ratings to hundreds of billions of dollars of bonds backed by risky mortgages and other loans that are now in many cases worthless.

The SEC said on Thursday that ratings agencies must reveal more information on past ratings so that investors could compare relative performance. Banks will have to share the underlying data used to determine ratings, so that competing agencies can offer unsolicited ratings for structured finance products.