The Blaugrana were handed a two-window transfer ban earlier this week, but the club has vowed to fight the sanctions.
However, Wenger, who clashed with the Catalans on numerous occasions over their public pursuit of former Gunners skipper Cesc Fabregas, believes they definitely did not follow protocol.
"It's certain that they haven't followed the rules," he is quoted as saying by Sport. "The rule is very clear: you cannot sign players under 16 unless their parents change residence for professional reasons.
"But it creates a debate - should parents change residence for professional reasons or not? What is not fair is that children under 16 move without their parents. This should be very clear."