_{So one of my opponents was elected on round one for Minster of Internal Security ( immediately destroy 4 GFs on Mecatol Rex). Currently Mecatol Rex is uncontrolled with Custodians protecting it. I am looking to invade MR soon so I imagine that this card will be used at some point very likely against me. So how would this work?}

_{Would my opponent be able to disrupt my invasion by killing my invasion forces or must he wait for me to actually take MR before destroying my GFs. The PC is played "immediately" when discarded so it is not the timing. The question is when are my GFs officially on the planet to fit the target restrictions. I suppose they literally are on planet in order to fight the invasion but I can also see that they should be in control of the planet as well. If the later is the case and 2 players were fighting on the planet could a third party play to destroy GFs from both players?}

I'd probably say "no". I'm not sure that the invading force is considered to be "on" Mecatol Rex during the invasion.

However, this probably would be good to have an official clarification for. I'll submit a question and report the response

I would say, yes he can. The rulebook (page 12) states that during phase 5 of the tactical action one lands GFs and PDS's from carriers onto the planet thus forcing an invasion. At this point (even before dice get rolled) they are considered "on-planet" and therefore are valid targets. Note that the card says "at any time" so he could play it after PDS fires at your lads, if he was defending and serious about it. Take your hits, chalk a tic in your "I-hate-you" column with his name on it, and rest assured that nobody can do it to you again.

I'm at work, does anyone have the card in front of them to look at. I would just say house rule that action cards can only be used between those involved in the combat. Nothing like having a player put experimental weapons on a station in a battle they are not even involed in.