According to attorneys, it may be illegal and sets a dangerous precedent to permit a large mine to continue operating months after its planning permission expired.
Tuesday saw the implementation of an enforcement notice giving the Ffos-y-Fran opencast mine in Merthyr Tydfil 28 days to stop mining coal.
Lawyers for environmentalists claimed that the Welsh government and Merthyr council should have intervened sooner.
The council, however, claimed that it had a "contrary legal view of the situation.".
The Welsh government declared that it wanted to put "a managed end to the extraction and use of coal," but the former said it would not comment further due to "potential litigation.".
A comment has been requested from mine operator Merthyr (South Wales) Ltd.
The closure of Ffos-y-Fran, the largest and currently final opencast coal mine in the UK, is also developing into a protracted saga.
Merthyr (South Wales) Ltd has until the end of July to cease all coal extraction after its request for a longer period of time was denied in April on the grounds of climate change.
It indicates that the mine, which is about the size of 400 football fields, will have had at least 10 months of operational time left after its planning permission expires in September 2022.
According to statistics, 199,307 tonnes of coal were dug up at the site between 7 September 2022 and 31 March 2023.
The planning system was "put in a bad light" as a result of the circumstance, according to barristers working with the advocacy group Coal Action Network in an open letter of legal advice.
According to Matthew McFeeley of the environmental law firm Richard Buxton Solicitors, "It certainly sends a signal to other operators who may be debating whether to shut down their coal mine or oil well – do they need to do that?
Without planning control, they might be able to extract for a long time. ".
Since several months ago, locals and campaigners have been protesting the situation by sending in images, videos, and drone footage of alleged mining.
It had been "incredibly frustrating," according to Chris Austin, 67, who lives close by the site.
He continued, "The local authority could have moved almost immediately, but they've been taking their time on this.".
It was crucial to the "elongated process" that followed, according to Dr. Neil Harris, senior lecturer in statutory planning at Cardiff University, that the application to prolong the mine's life was submitted just days before its planning permission expired.
The council may have come across as "a little cautious," but he suggested that this was due to the council's desire to make the best choice possible in a "really complicated case" and avoid opening itself up to legal scrutiny.
In a previous statement, Merthyr (South Wales) Ltd. stated that it and the council were in "active discussion" regarding "a safe cessation of coaling" and ongoing restoration.
In addition to supplying the steelworks in nearby Port Talbot and the UK's historic steam railways, the site has 180 employees.
We have a different legal perspective on the situation, according to a Merthyr council spokeswoman. Further commentary is inappropriate in light of potential legal action. ".
We want to put a controlled end to the extraction and use of coal, according to a Welsh government spokeswoman.
"To preserve a Wales we can be proud of, we must act quickly and seriously in the face of a climate and natural disaster.