Environmentalists fear the new plants will pump millions of tons of pollutants into the air every year.
"Coal plants seem so archaic," said Stacy Foss, a teacher who brought her two young children to the rally Sunday in the 50-degree weather. "Texas is so environmentally incorrect."
Energy giant TXU Corp., which wants to build 11 of the new plants, has said the facilities will meet the state's growing demand for power, give an economic boost to small towns and reduce toxic emissions by replacing older, less efficient plants.
The TXU proposal is on the fast track under an order Gov. Rick Perry issued in 2005 to expand the production of electricity and lower its cost.
Those attending the rally, organized by about 40 environmental and health advocacy groups, including the Sierra Club and the American Lung Association, called on lawmakers to support a time out on permits for the new plants.
A hearing on TXU's application is scheduled to begin Feb. 21.
TXU spokesman Tom Kleckner said the coal plants would be cleaner than environmentalists fear.
"These are not your grandfather's coal plants," Kleckner said as he surveyed the signs and listened to the speakers from the perimeter of the rally.
A coalition of business and energy interests recently bought more than $1 million in newspaper advertising to speak out against the coal plants and promote the rally. The Texas Clean Sky Coalition included at least one competitor of coal-fired plants - Chesapeake Energy Corp., a natural gas company in Oklahoma City.
Other opponents of the plants include 17 mayors whose cities are downwind of the plants, including Dallas Mayor Laura Miller and Houston Mayor Bill White.
"They'll burn 80 percent cleaner than today's coal plants," he said.
State Rep. Charles "Doc" Anderson has filed a resolution calling for a 180-day moratorium on new coal plant permits to give state officials more time to study environmental and health impacts.
"A moratorium would give us time to take a deep clean breath," Anderson said.
His resolution hasn't been scheduled for a vote in the House.
Many in the crowd Sunday carried signs warning about global warming and called for the state to invest in wind and solar power and conservation programs.
Several people dressed in costumes as coal miners with sooty faces. Damon Jones, an Austin restaurant manager, wore a gas mask with his black suit.
"I'm just another guy trying to avoid the pollution," Jones said.
Stephen Hodgsen, an engineer from Galveston, said he became motivated after watching former Vice President Al Gore's Oscar-nominated documentary about global warming, "An Inconvenient Truth."
"That showed me we need to do something," said Hodgsen, who supports more use of wind power and nuclear energy.
Marc Scott, a farmer who lives within just a few miles of four of the proposed plants, worries his family's health would suffer from air and water pollution.
"We're at ground zero," he said. "It won't matter which way the wind blows."
By Jim Vertuno