Aberthaw Power Station set to close, risking 170 jobs
Wales' last coal-fired power station looks set to close in March due to "market conditions", putting about 170 jobs at risk.
RWE said it was proposing closing the 1.56-megawatt Aberthaw B Power Station in Vale of Glamorgan on 31 March.
It will now consult staff and their representatives but the closure would not affect the amount of energy provided to the market, RWE said.
The Unite union said it was asking for an urgent meeting with management.
The plant, which opened in 1971 at a cost of more than £50m, was due to remain in operation until 2021.
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It used 3.5 million tonnes of coal in 2013, but that amount had fallen significantly by the time RWE decided to only generate electricity when needed, such as in the winter months, from April 2017.
"This is a difficult time for everyone at Aberthaw Power Station," said Roger Miesen, CEO of RWE Generation.
"However, market conditions made this decision necessary."
Unite's regional officer Kelvin Mawer said: "We will be asking for an urgent meeting with the management of RWE Generation for them to explain the earlier than expected closure of the plant.
"We want to know why the closure of the plant has been brought forward to next March from the anticipated date of 2021."
In 2016, the European Court of Justice (ECJ) found the Aberthaw plant had been emitting illegal levels of pollution.
Friends of the Earth, which has long called for the plant's closure, welcomed the announcement and called for more investment in green energy.
Haf Elgar, director of Friends of the Earth Cymru, said: "The writing's on the wall for the coal industry - we cannot keep burning fossil fuels in a climate emergency and we must stop now."