Anderlecht have been fined 50,000 euros (£43,900) and banned from selling tickets to their travelling fans for two European matches following crowd trouble at West Ham last week.
European governing body Uefa imposed the sanctions for the "lighting of fireworks, throwing of objects, acts of damage and crowd disturbances".
One supporter was sentenced to eight weeks in prison following the ugly scenes during the Europa Conference League match at London Stadium, for which the Belgian club has apologised.
The second match of the ban is suspended for two years.
Seats were thrown and flares set off by some Anderlecht supporters during West Ham's 2-1 victory on 13 October.