French authorities have opened an investigation into a Nazi-themed party that led to the firing of a British lawmaker who attended.

Aiden Burley, 32, a Conservative member of Britain’s House of Commons, was dismissed in December, a week after photos of his presence at the stag party at a French ski resort came to light. At least one party participant dressed up in an SS officer’s uniform, and the guests toasted to the Nazi Party and the Third Reich.

It is illegal in France to wear or exhibit in public Nazi-era memorabilia or copies of such memorabilia.

Burley and 12 other guests could face charges in France of defending war crimes or crimes against humanity and inciting racial hatred. They could face six months in prison and large fines.

Burley apologized following the incident with an “unreserved, wholehearted and fulsome apology” in a letter to the London-based Jewish Chronicle newspaper.

Prime Minister David Cameron ordered a full investigation into the incident following reports that Burley had been responsible for ordering the SS uniform costumes. Cameron dismissed Burley from his post as a parliamentary aide to the transport secretary.