The Spanish football federation (RFEF) said on Saturday that there would be no restrictions on players from outside the EU for the Super Cup, despite only three being allowed in squads for league matches.
Sevilla said they could file a complaint if Barca name an "improper lineup" in Tangier, Morocco.
"Sevilla FC is surprised by the RFEF's announcement 24 hours before the Super Cup," Sevilla said in a statement.
"It has said that as many non-EU players as desired can be registered. In their last statement for the 2018-2019 season, only three were due to be allowed, without exception.
"The club's legal department is studying the matter and should FC Barcelona submit a team with more than three non-EU players, it would present possible ground for the filing of a complaint on account of an improper line-up."
New signings Malcom, Arturo Vidal and Arthur will likely be Barca's three non-EU players on Sunday, although Brazilian centre-back Marlon has also travelled with the squad.
Philippe Coutinho has reportedly acquired a Portuguese passport through his wife in the last week, while his fellow South Americans Lionel Messi and Luis Suarez are already EU citizens.
Sevilla qualified for the match as last season's Copa del Rey runners-up, after Barcelona won the league and cup double.