UEFA have confirmed they have opened disciplinary proceedings with Hungary, Belgium and Portugal following crowd disturbances across games on Saturday.
A group of around 200 Hungary fans broke through flimsy segregation before their 1-1 draw with Iceland at the Stade Velodrome, charging from one end of the stadium to another and clashing with stewards.
Flares and firecrackers were also lit after Birkir Saeversson's 88th-minute own-goal, which left Hungary top of Group F with one game to play.
UEFA are looking into the "setting off of fireworks", "throwing of objects" and "crowd disturbances" by Hungarian supporters.
Marseille's stadium has previously seen similar trouble in the tournament, when Russia supporters broke through segregation to attack England supporters after their 1-1 draw last weekend.
The Russian Football Union were given a €150,000 fine and a suspended disqualification from the tournament after the incident - which followed a day of fighting between Russian fans, their English counterparts, local gangs and police.
UEFA will rule on a suitable punishment for Hungary on Tuesday.
Fireworks set off by Belgium fans during their 3-0 win over Republic of Ireland could also land their federation in trouble, while Portugal's authorities have questions to answer after a fan came on to the pitch after their 0-0 draw with Austria at the Parc des Princes to take a photo with Cristiano Ronaldo.