They are worried that Belene, would only increase Bulgaria's reliance on energy from Russia, which currently supplies almost all of the gas the country needs.
Although denying any pressure on Sofia to abandon Belene, Washington is lobbying for Bulgaria to resume the search for alternative energy sources, such as shale gas.
The government froze plans to finish the plant at Belene last year, when work at the site on the southern bank of the River Danube was already well under way.