(CNN) Serbia's national soccer team has been ordered to play its next home game behind closed doors after UEFA decided to punish the "racist behavior" of its supporters.

European football's governing body had been investigating what happened in Belgrade's Stadion Rajko Mitić during Serbia's 4-2 defeat by Portugal in September and announced its decision Monday.

UEFA ruled that Serbia must play two of its next home games without supporters, with the second game suspended for a one-year probationary period.

The Serbian FA will also have to display "#EqualGame" banners around the stadium during its next home game -- a crucial Group B qualifying match against Luxembourg on November 14. Serbia currently has 10 points, one behind second place Portugal, with Ukraine topping the group with 19 points.

Serbia's Football Association was also fined $37,000 (€33,250) for a number of other charges including illicit chants and field invasions.