Bendtner is suspected of breaking Law 4 of football regarding players' kit and equipment, UEFA said in a statement. The football body's disciplinary panel will deal with the case Monday.
The striker lifted his shirt and lowered his shorts slightly, revealing the name of a betting firm across the top of his underpants, after scoring his second goal in a 3-2 loss against Portugal on Wednesday.
UEFA tournament rules for Euro 2012 also bar any sponsor advertising on players' kit.
Earlier Friday, Bendtner flashed his fresh, regulation-friendly black underpants at training, which should keep him within team and UEFA guidelines.
Bendtner got a dressing down from the Danish Football Association on Thursday for flouting team policy. The association has official ties to a rival gambling company.
Danish team officials have told Bendtner he must abide by rules with his match-day underwear when Denmark plays Germany in the final round of Group B matches on Sunday in Lviv, Ukraine. Germany tops the group with six points while Denmark and Portugal both have three. The Netherlands is last with zero points.