The DRC government last week suspended Chinese-owned TTT Mining and Huaying Trading Co. for failing to ensure their work wasn't benefiting armed rebels in the country.
"The Congolese government's decision to suspend minerals traders for failing to do due diligence sends a strong message to other companies exporting minerals from eastern DRC that they must source responsibly, or face sanctions," Global Witness campaigner Sophia Pickles said in a statement.
Kinshasa in February passed a measure requiring mining and mineral trading companies to comply with standards outlined by the Organization of Economic Cooperation and Development.
Conflict in DRC is on the rise following a mutiny waged by rebel Gen. Bosco Ntaganda, wanted by the International Criminal Court for alleged crimes against humanity.
Global Witness says Ntaganda and his supporters were able to reap the benefits of DRC mining by controlling key lease areas.
"This latest insurgency stands to be financed by a war chest filled with proceeds from their illegal involvement in the minerals trade," said Pickles.