DALLAS -- Environmental groups said Tuesday they filed motions requesting that state regulators reconsider their approval of a permit allowing TXU Corp. to build a new coal-fired power plant in Central Texas.

The groups, which include the Texas Clean Air Cities Coalition, said in a statement the motion could be the first in a series of challenges to prevent construction.

Last month, the Texas Commission on Environmental Quality voted 2-1 to approve an air permit for the two-unit plant in Robertson County, about 100 miles northeast of Austin.

Environmentalists fear the plant will foul Texas skies and pump 1,440 pounds of mercury into the air each year.

Two administrative law judges recommended last year that the air permit be denied, saying TXU failed to prove it could meet emissions limits.

The reahearings are a necessary step before lawsuits against the commission in state or federal court can be pursued.