New information that the U.S. Environmental Protection Agency released on Oct. 28 could signal changes it might make to a proposed major rule that aims to cut greenhouse-gas emissions from existing powerplants, EPA watchers say.

The shape of the final regulation is significant for engineering and construction firms that will help states and electric utilities to implement plans and controls to trim carbon emissions. Some construction-industry groups and labor unions have said the proposal could shutter coal plants and cost jobs in states in which coal is a major power-generation source. They also contend it could cause grid-reliability concerns.