Anheuser Busch's Budweiser s the official beer for the tournament and world football's governing body fiercely protects its sponsors from brands which are not FIFA partners.
Dutch fans are famed for their outlandish orange outfits but the group of women seated together, clapping and swaying in unison, and wearing the dress produced by brewer Bavaria caught the eye of experts on the look out for such campaigns.
Bavaria has clashed with FIFA before over supporters wearing its orange clothes to stadiums.
Four years ago at the Germany World Cup scores of Dutch men watched the Netherlands play in a Stuttgart stadium in their underwear after stewards ordered them to remove orange lederhosen bearing the name of Bavaria.
"What seems to have happened is that there was a clear ambush marketing activity by a Dutch brewery company," FIFA spokesman Nicolas Maingot said on Tuesday, adding they later asked the women for details.
South Africa has particularly strong laws to protect intellectual property and to punish "ambush marketing" where non-affiliated companies try to use the World Cup brand.
Bavaria board member Peer Swinkels told Reuters that FIFA's reaction was ridiculous.
"FIFA does not have the monopoly on orange and people have the freedom to wear what they want ... This year we even decided to take out the brand name on these dresses because of what happened four years ago."
