Ontario's Liberal government has pledged to shut the coal plants by 2014.
But an election is looming in this fall, campaign spokesman Gideon Forman said in an interview.
"We don't know who's going to be in government in October 2011," said Forman, who is executive director of the Canadian Association of Physicians for the Environment.
"It's quite possible that we could have another government that would not embrace the coal phase-out and we're quite concerned about that."
"We want whoever's in power to know that doctors and nurses support this."
The Conservatives have been highly critical of the Green Energy Act, which seeks to replace coal with renewables and conservation.
The ads back renewable power.
"Ontario doctors, nurses and other health professionals support energy conservation combined with wind and solar power, to help us move away from coal," the ads say.
Critics of wind power have said that wind turbines can damage the health of those who live nearby.
Forman questions the evidence for that. But even if true, he said, pollution from coal plants causes much worse damage, leading to 150,000 illnesses and 300 deaths each year in Ontario.
Wind power critics have also said that gas-fired plants must be built to offset the variability of wind. Forman said that a mature renewable power sector with solar, wind and geothermal power can provide stability.
Forman says the exact cost isn't yet tallied, but the ads will cost in the "tens of thousands of dollars."
The groups running the ads would like to see the coal plants phased out even earlier than 2014, Forman said.
The college of family physicians has 10,000 members and the nurses' association has 31,000 members.
"All the research we've done shows that coal has to go."