Advocacy group Global Witness challenged a report published in the Philosophical Transactions of the Royal Society stating deforestation in the Congo River basin was slowing down because of effective timber management. The advocacy group said the study ignored issues like illegal logging in the region.
Advocate Alexandra Pardal said in a statement the rainforest was diminishing at a rate of 770 square miles per year.
"This is totally unsustainable, and it's set to get worse," she said Monday. "The idea that things are moving in the right direction is ludicrous."
The European Union in March passed legislation meant to thwart the flow of illegally harvested timber into the eurozone. Researchers told the BBC the rate of decline was slower than the 1,100 acres of forest lost during the 1990s.
A BBC investigation published Sunday suggests loggers in the Democratic Republic of Congo are maneuvering around EU restrictions to continue harvesting parts of the area considered off limits.
Logging companies who spoke with the BBC denied the allegations though advocates say more investigation is needed at the very least.
The Congolese rainforest covers more than 800,000 square miles and is the second-largest in the world after the Amazon.