However, the FERC said that its staff has "serious concerns" regarding the magnitude of the largest spill, "its environmental impacts, the lack of clarity regarding the underlying reasons for its occurrence, and the possibility of future problems."

It said that the largest spill was "several orders of magnitude greater than other documented inadvertent returns for this project."

The commission, which regulates all natural-gas pipelines, said that "a stoppage of additional drilling is warranted to facilitate a review of Rover's efforts to search for and locate any potential releases."

The Ohio EPA has fined Energy Transfer Partners about $400,000 and has asked the FERC for support. Craig Butler, the Ohio EPA director, said the company's response had been "dismissive," "exceptionally disappointing" and unlike any other response he has seen from a company in his 27 years at the agency.

The Rover pipeline is $4.2 billion project that would link the shale-gas-rich regions of Appalachia to Michigan and Ontario.