The U.S. Securities and Exchange Commission announced Tuesday that it had charged four underwriters with failing to comply with municipal bond offering disclosure requirements.

The regulator filed a litigated action against Oppenheimer & Co. Inc. OPY, -4.15%, while announcing settlements with BNY Mellon Capital Markets BK, +0.16%, TD Securities LLC TD, -3.03% and Jefferies LLC for selling new issue municipal bonds without obtaining required disclosures for investors.

“I applaud the excellent work of the Division’s Public Finance Abuse Unit in bringing these first-ever actions in the $4 trillion municipal bond space,” said Gurbir Grewal, director of the SEC’s Division of Enforcement, in a statement. “We encourage underwriters to examine their practices and to self-report any failures to us before we identify them ourselves.”

As a result of the findings of the investigation, the SEC said it has begun investigations of other firms’ practices in this area.