When the National Party began its campaign against the Electoral Finance Act, they argued that they were "protecting free speech" and "defending democracy". This has now led them to argue that encouraging people to participate in the democratic process by writing to MPs is illegal in election year. I guess they must really not like what the public is telling them...
But quite apart from being absurd, hypocritical, and anti-democratic, National is simply flat-out wrong on this. In order for material to be classified as an "election advertisement" and hence require a promoter statement, it must encourage people to vote either for or against a candidate or party, either explicitly (e.g. by saying "don't vote National"), or "by reference to views, positions, or policies that are or are not held, taken, or pursued". CAFCA's postcards certainly don't do the former, and cannot reasonably be regarded as doing the latter. They're not aimed at influencing the votes of members of the public, they're aimed at influencing the policy positions of MPs. But I forget - according to National only the rich ought to be allowed to do that.
So why is National so upset by this? Firstly, as I mentioned above, they clearly don't like what the public is telling them. But more importantly, the last thing National wants is an active, engaged, interested public which is actually thinking about the issues. If they did, they'd be releasing policy...