Mills said Vettori was uncomfortable with a particular clause in the contract that stipulates that "the player is not allowed to play for any other team that may at any point of time qualify for the Champions League".
Mills said NZC is overlooking the fact that if Vettori signs his current IPL contract then he would not be able to play for Northern Districts if they qualified for the Champions League.
This concern is somewhat ridiculous. Obviously, no team will want to sign a player if he is going to run away when the Champions League comes around. Since the closest analogy is European football, let's look at that.
If a player signs for a club (say, Ronaldo for Manchester United), he is obligated to play for Manchester United till either his contract runs out, or he is sold to a different club, whichever is earlier. Selling here implies that all three parties (Manchester United, Ronaldo and the other club) agree on the sale (and all its specifics). If Manchester United qualify for the European Champions League, Ronaldo MUST play for Manchester United, even if Sporting Lisbon from Portugal (Ronaldo's childhood club) qualify for the event. Once he has signed for Manchester United, he has no connection with Sporting Lisbon and the question of playing for them does not arise.
Further, if Ronaldo moves to a different club in the middle of the season, he is also cup-tied. Which means that if he has played for Manchester United in any cup competition (Champions League, FA Cup, League Cup), he cannot play in that competition for his new club that season. He can play in those cups starting from the next season. In fact, being listed in Manchester United's roster for the Champions Leauge is enough to make him cup-tied for the Champions League. (League games are not classified as cup competitions, and the player can play in league games for the new team.)
While the merits and demerits of making a player cup-tied can be argued over, the important point here is that Ronaldo cannot play for any club other than Manchester United as long as his contract with them is valid. So, why should it be any different in cricket? Granted that the European/US styled league model exists only in India at present. But since teams from many local leagues do feed into the Champions League, it stands to reason that a player should be eligible to play only for one team at a time.
I do grant Mills one point though. If the IPL team Vettori signs for agrees to release him for Northern Districts, there should not be a problem with Vettori representing them in the Champions League. Which is prevented by the MOU. But then again, the IPL teams are only franchises (US style), and not clubs in their own right (European style), which means the IPL can introduce such restrictions and get away with it legally!