Police in Merthyr Tydfil said they had to move vehicles and disperse crowds after a late night gathering outside a centre used for coronavirus testing.
Officers were called to outside the Leisure village on Sunday night.
They gathered evidence using body word cameras so that retrospective enforcement action can be taken against those individuals who were involved.
A spokesman said that work has already begun to identify those who attended – and they face being issued with a Section 59 warning and risk having their vehicle seized.
He added that anybody identified will also be issued with a fixed penalty notice for breaching Welsh Government coronavirus regulations.
Local Policing Inspector Jonathan Duckham, said: “The large gathering caused a significant amount of concern for residents and disrupted local roads.
“What happened was a blatant disregard for the current restrictions which prevent people gathering in that manner and anybody identified will be appropriately dealt with.
“We will be increasing patrols and monitoring the area and will not hesitate to take action should any further incidents occur.”
The leisure centre is being used as a centre for mass testing that is taking place in the county borough.
Anyone with information should contact police on 101.