Sustainable investor groups are urging the Securities and Exchange Commission not to let a recently filed lawsuit delay the agency from implementing a rule that requires U.S. companies to report whether they are using minerals from the Congo and fueling violence there.

The lawsuit, filed by the U.S. Chamber of Commerce, the National Association of Manufacturers and the Business Roundtable in the U.S. Court of Appeals in the District of Columbia, seeks to stop the implementation of the "conflict mineral" rule that the SEC developed as required under provisions of the 2010 Dodd-Frank Act.

The investors, who oppose the lawsuit, want the SEC to vigorously defend itself and reject any requests for a stay of the rule's requirements.

In August the SEC approved the rule, which requires U.S. companies using gold, tin, tungsten and tantalum in their products to make "reasonable" efforts to determine if those materials came from the Democratic Republic of Congo or an adjoining country, Bloomberg News reported. Those minerals are used by thousands of U.S. companies to make products that range from smartphones to jewelry to cars. Companies are required to file their first reports on the minerals in 2014, but they maintain the requirements are too expensive and will be ineffective at controlling the violence.

The investor group notes in a November 30 letter to the SEC that violence is escalating in the Democratic Republic of Congo. Tens of thousands of people were forced to flee the city of Goma when it fell last month to M23 rebels. On Nov. 13, the U.N. imposed sanctions on M23 commander Colonel Sultani Makenga for violations of international law, including rape and the use of child soldiers, according to Bloomberg News.

"Conflict minerals disclosure is material to investors and will inform and improve our ability to assess social (i.e., human rights) and reputational risks in an issuer’s supply chain," the letter says. "The final rule offered the unique opportunity to make conflict mineral related disclosures consistent and accessible to all investors, thereby improving efficiency in U.S. markets in allocating capital to issuers with the best overall prospects for longā€term shareholder value. The suit brought by these industry groups therefore conflicts with our interests and the protection of investors."

Investor groups signing the letter include Lauren Compere, director of shareholder engagement at Boston Common Asset Management; Bennett Freeman, senior vice president of sustainability research and policy at Calvert Investments; Patricia Jurewicz, director of the Responsible Sourcing Network, a project of As You Sow; and Lisa Woll, CEO of US SIF: The Forum for Sustainable and Responsible Investing.