The new £1bn Pembroke power station may be forced to change its cooling system because of fears its technology may breach conservation laws.
A leaked document seen by BBC Wales says the European Commission is so concerned it has sent a formal notice of infringement to the UK government.
It lists 18 violations of four separate environment laws.
But RWE npower, which built the power station, said the plant's development had been thoroughly scrutinised.
Pembroke's gas-fired power station is Britain's latest and was officially opened by UK energy minister John Hayes last September.
Three months on, the European Commission is asking the UK government to prove the technology used at the plant will not adversely affect Pembrokeshire.
Read more on this story on BBC Wales News.
