The gesture made by Granit Xhaka and Xherdan Shaqiri - open hands together with the thumbs interlocked and fingers outstretched - resembled the double-headed eagle, which is displayed on Albania's national flag.
If found guilty, both players could face two-match bans which would rule them out of Switzerland's final group match against Costa Rica on Wednesday, and a possible last 16 match.
Xhaka and Shaqiri are both ethnic Albanians from Kosovo, which broke away from Serbia in war in 1999 and declared independence nearly a decade later but is not recognised by Serbia.
Granit Xhaka and Xherdan Shaqiri received a warning and a fine of 10,000 Swiss francs, or about $10,100, for unsporting behavior, in a judgment Monday by FIFA's disciplinary panel.
Arsenal midfielder Xhaka's father spent three and a half years as a political prisoner in Yugoslavia, while Shaqiri was born in Yugoslavia before emigrating to Switzerland as a child.
According to an official statement, Federation Internationale de Football Association has launched an investigation into Lichtsteiner's behavior when he was celebrating one of his side's goals, while Kokeza and Krstajic are being scrutinized due to their remarks after the match, which may have been inappropriate.
ETHIOPIA: Grenade blast at new Prime Minister's rally; one dead
The United States has been among other nations expressing support for the changes in the country, a key security ally. Ethiopia's government has given few details of the incident, which Abiy blamed on "anti-peace forces".
Serbia does not recognise Kosovo's independence and relations between the two countries remain tense in the wake of a war in the late 1990s.
Swiss captain Stephan Lichsteiner was also fined 5,000 Swiss francs [4,300 euros] for joining in the celebration.
Serbia saw their lead evaporate in a fiery 2-1 defeat to Group E rivals Switzerland in Kaliningrad on Saturday (AEST).
Croatia's FA was fined 13,000 Swiss francs after its fans were involved in fights and throwing of objects during the same game.
Media reports quoted Krstajic as telling Serbian reporters that German referee Felix Brych, who denied his team a penalty, should be put on trial in The Hague, home of the United Nations' war crimes tribunal for the former Yugoslavia.
26-year-old Shaqiri, who plays for Stoke City, said after the match that "it's just emotion" when he was quizzed about the way he celebrated. Shaqiri had posted a photograph on Instagram of his playing boots, one with a Switzerland flag on the heel and the other with a Kosovo flag.