Talks this week with Italian authorities failed to show they were adhering to EU waste management laws to resolve a festering garbage collection crisis in the southern Italian city, EU spokeswoman Barbara Helfferich said.
The European Commission said it has demanded "speedy compliance" with EU law and proof within a month that officials are taking steps to clear the trash, she told reporters.
Some 250,000 tons of backlogged trash has been piling up on the streets of Naples since collection came to a near halt in December.
Collectors have stopped picking up garbage in Naples and the Campania region because there is no more room for the trash at dumps.
The region has long been plagued by garbage crises. Dumps are packed to overflowing, and local communities have blocked efforts to build new ones, citing health risks.
EU Environment Commissioner Stavros Dimas already has threatened Italy with fines to force it to comply with waste management rules. He has called for Italian authorities to set up a long-term strategy to deal with the region's waste.
"The situation in Campania is intolerable and I fully understand the frustrations of residents who fear for their health," Dimas said.
EU officials said a waste management plan for Campania was adopted more than a decade ago but never properly implemented.
The Italian government, harshly criticized for failing to clean up the streets of Naples, has appointed a commissioner to deal with the crisis. But the streets have yet to be fully cleared of the heaps of garbage that have piled up for weeks.
Authorities and residents have blamed organized crime infiltration of garbage collection services, disorganized bureaucracy and protests that hinder the construction of dumps and disposal plants.
Some Italian regions have recently volunteered to take Neapolitan garbage.