The company told the Baltimore Sun it had notified the region’s grid operator of its intention to idle the Prince George’s County and Montgomery County complexes, which are two of just seven remaining coal plants in the state.

NRG cited the rise of more cost-effective natural gas and the potential for more stringent environmental regulations for its decision.

“It simply wouldn't be economic, given market conditions and the pressure that is on coal plants right now,” company spokesman David Gaier told the paper.

“We'll obviously continue to evaluate our options.”

He also noted that its deactivation notices could be rescinded should it change its mind.

The five total units, all about 50 years old, produce a combined 1200MW of electricity annually.

Sierra Club environmentalists cheered the move.

“Passionate citizens from across the state have been the driving force in our fight to fundamentally change the way Maryland produces and consumes energy,” Sierra Club Maryland board member Donna McDowell said.

“Maryland is simultaneously helping to lead the nation in new 21st century clean energy investments like offshore wind while ensuring cleaner air for all and replacing dirty, outdated coal plants.”

The group claimed air pollution from the Chalk Point and Dickerson coal plants contributed to 42 deaths and 680 asthma attacks annually, citing data from the Clean Air Task Force.