The strains between Government allies New Zealand First and the Greens further intensified last night, as MPs from both sides lobbed grenades into each other's camps.
The latest skirmish is over the so-called waka-Jumping legislation – the repealing of which passed its first reading in the House last night.
NZ First leader Winston Peters told the Herald the Greens have not kept their word and are betraying Labour.
But, Shaw – the Greens' co-leader – said his party's hands are clean and he was under no obligations to vote against the law's repealing.
The Greens had begrudgingly supported making the bill into law two years ago, but made it clear they were not happy to do it.
But they were bound to it, because of their supply and confidence deal with Labour which made it clear the bill had to be supported by all three governing parties.
Speaking to RNZ this morning, Shaw said his party was obligated to support the bill – as per their agreement – but there was nothing in that agreement that said they were not allowed to support its repealing.
The bill – officially called the Electoral Integrity Amendment Bill – requires MPs who quit, or are expelled from a party, to leave Parliament more or less on the spot, instead of joining, or forming new parties.
In the past, the Greens have called this "undemocratic".
And in the House last night, they voted with National to have the law scrapped.
"We have learned that it is the letter of the agreement, rather than the spirit of the agreement, that's what counts when it comes to New Zealand First," Shaw told RNZ.
On a number of occasions – including the canning of a capital gains tax and the blocking of Auckland light rail this term – NZ First have withheld their support, as they were not in the coalition agreement.
"When it comes to the repeal of the party hopping bill, I would say we have observed exactly the letter of our agreement," Shaw said.
Asked if he was playing the same political games as Peters, Shaw said: "I learn from the master".
Peters, however, was not impressed with Shaw's logic.
"That's the defence of someone who hasn't got his thoughts or planning together when he did the arrangement in the first place.