As coal and nuclear power plants around the U.S. close due to competitive pressures, the number of people employed in making electricity is shrinking.

Older power plants are being retired at an unprecedented pace as power producers wage a fierce fight for market share. They are being supplanted by newer power plants fired by natural gas, as well as wind and solar farms, which often are simpler to operate and require fewer workers.

The Center for Energy Workforce Development, a group backed by six major utility industry groups, estimates that total direct utility employment has fallen to 505,000 from 550,000 since 2006. That is eroding a stable source of well-paying jobs, especially in rural areas, and generating local political pressure at a time when President Donald Trump has made blue-collar job retention a major issue.

Many industry leaders believe the shift is inevitable.

“The power sector is just not going to contribute to the economy in terms of jobs the way it once did,” said Curt Morgan, president and chief executive of Vistra Energy Corp , the electricity producer which used to be part of the former Energy Future Holdings Corp., and is planning to merge with rival Dynegy Inc.