The U.S. Securities and Exchange Commission's potential suspension of Standard & Poor's from grading commercial-mortgage backed bonds would threaten a practice regulators have blamed for fueling the credit crisis.

The SEC has been investigating whether the firm bent ratings criteria to win business in 2011, according to a person with knowledge of the matter, who asked not to be named because discussions between the agency and S&P about a possible suspension are private. In a practice known as ratings shopping, banks often seek assessments from several credit graders and choose the ones that give the most favorable views when assembling asset-backed bond deals linked to everything from auto loans to mortgages.

"Even temporarily taking away a slice of S&P's business would send a powerful message to the rest of the market that the SEC is serious about attempting to address ratings shopping," said Jeffrey Manns, an associate professor of law at George Washington University in Washington.