The new body represents mining companies accounting for 80% of copper and cobalt production and 90% of gold production in the country, including Randgold Resources, Glencore, Ivanhoe Mines, Gold Mountain International, Zijin Mining Group, MMG Limited, AngloGold Ashanti, Crystal River Global and China Molybdenum Co.
The code is set to increase royalties, introduce a super profits tax and remove a 10-year amnesty on new rules for existing miners.
General secretary of the new body, Richard Robinson, said the main issue was still the application of the code, which compromised "investors who have invested in the country individually and alongside state companies, on terms guaranteed by the government through legislation, specific guarantees and bilateral trade agreements".
"Furthermore, should some of the key issues in the new code not be addressed it would discourage further investment in large and small sustainable projects, which is crucial for the DRC economy as well as the mining sector," he said.
Robinson said the MPI was committed to continue working with the government to come to a "mutually agreeable solution and improve the legal framework for current and new investments".
The aim is to find a sustainable outcome for all DRC stakeholders, while also respecting the country's laws and preserving acquired rights.
Individual companies were also continuing to engage with the authorities with regard to the effect and implementation of the code.