No orders were actually violated. No one from Starfleet warned the Cardassians of the Klingon invasion.
Um, the VERY literal "letter of the law" may not have been violated, but Sisko(of Starfleet) pretty clearly warned Garak(a Cardassian with connections) of the Klingon invasion.
How well do you think Sisko's defense of "I was having a conversation while my tailor measured me" would hold up to Starfleet Command?