It's more than likely not voluntary, more often than not these NGO's (so called) are up to their necks in government in one way or another, and they use tax money (ie money gained through coercion).
Discussion
Yeah that sucks. Farce of a designation.
I hate that worthwhile charities and initiatives that genuinely do not receive funding from the Government get bundled up with these multi-departmental monstrosities that do.
But alas, I am one man ranting into the wind . . .
It's even far worse than that in California the way charities are regulated. I'm with you.