Worf gets away with a lot of things that would violate the Prime Directive in regards to the Klingon Government because he has dual citizenship and is a member of Klingon nobility.

Even with Worf being a Klingon, and a recognized member of Klingon society, he still had to resign his commission to leave the Enterprise and go fight for Gowron's forces in the civil war against the Duras' sister's supporters.

Worf: Captain, we must intervene. The Duras family is corrupt and hungry for power with no sense of honour or loyalty. They represent a grave threat to the security of the Federation. Captain, you and I know that they have conspired with Romulans in the past. If they should be victors in this war, they will surely form a new Klingon-Romulan alliance. That would represent a fundamental shift of power in this quadrant. Starfleet must support Gowron. It is in the interests of both the Federation and the Empire. I beg you, support us in our cause.
Picard: Mister Worf, I don't have to lecture you on the principle of non-interference. As Starfleet officers, we have all sworn an oath to uphold that principle whatever our personal feelings. I'm sorry. I must refuse your request.
Picard: Mister Worf. I'm afraid I must recall you to duty. The Enterprise will be leaving this sector immediately.
Worf: Captain, I respectfully request that I be allowed to take an extended leave of absence.
Picard: Mister Worf, your responsibilities as a Starfleet officer are incompatible with remaining on board a Klingon ship during a time of war.
Worf: Captain.
Picard: I order you to return to duty at once.
Worf: Then I resign my commission as a Starfleet officer.

They just conveniently forget that's the case in the final scene of "Redemption II" when Worf asks Picard for permission to return to duty. Guess he never got around to filing the paperwork.