The last coal-fired power station in Wales is to close.
The Aberthaw station, near Barry will close in 2020. Power giant RWE, who own the station, said it faced "challenging market conditions".
A consultation with affected staff and employee representatives will now begin.
The 1,560MW Aberthaw B power station , which opened in 1971, directly employs around 170 people.
RWE Generation CEO Roger Miesen said: “This is a difficult time for everyone at Aberthaw Power Station.
"However market conditions made this decision necessary. I would like to thank all of our staff, past and present, who have contributed to the success of the station for so many years. Over the coming months we will complete the consultation process."
The proposed date of closure is March 31 2020.
RWE said: "The decision to close the station will contribute to the company’s goal to reduce its CO emissions step by step."
Campaigners have long called for the plant to be closed, claiming it cost more in pollution than the gains it generates in jobs and electricity.
In 2015 the The European Commission announced it was taking the UK Government to court because the pollution emitted by Aberthaw power station was above legal limits.
In the same year the UK Government said all coal-fired power stations must close by 2025 and will be restricted in their usage from 2023.
Aberthaw once described itself as "one of the most efficient coal-fired power stations in the UK".
A 2015 report by Greenpeace and Friends of the Earth said Aberthaw, which can produce electricity for 1.5m homes, had the third highest emissions of nitrogen oxides of any industrial installation in the whole of the European Union.
"Hundreds of people's lives are ended prematurely as a result of pollution from Aberthaw power station every year," the report said. "This pollution also causes tens of thousands of days of lost productivity through sick leave, and hundreds of thousands of days of illness every year.
"The pollution is responsible for causing asthma symptoms in children, bronchitis in children, chronic bronchitis in adults, hundreds of hospital admissions every year, and low birth weight in babies. Over the 45 years since it started operating, pollution from this one power station alone is likely to have caused the premature deaths of more than 3,000 people in Wales, and 18,000 across a wider area."
At the time Aberthaw said it was fully compliant and was "vital" to the UK's electricity supply.
