Not being Government bills, they are not subject to being passed under urgency, which soon stifles Opposition MPs' appetites for a filibuster.
With Parliament scheduled to rise in early October before the general election, Labour has been punting on those Wednesdays running out before the voluntary membership bill can be passed.
But if that happens, the legislation will almost certainly be carried over to the next Parliament. Unless Labour wins the election - which is looking highly unlikely - the bill will ultimately become law anyway.
That is for the future. What matters now is that last Wednesday things shifted from straight filibuster to pure farce. The only characters needed to make this Trevor Mallard-orchestrated protest a complete pantomime were Chuckles the Clown and Dorothy the Dinosaur.
Labour not only demeaned itself, again - something it is perfectly at liberty to do - it also demeaned Parliament, and that is unacceptable.
For the best part of an hour, Labour MPs raised timewasting points of order and forced a series of pointless votes to try to stop debate on Roy's bill from even starting.
Labour made repeated demands that Speaker Lockwood Smith be recalled to the chamber to rule on decisions made by National's Eric Roy, who was chairing the House.
This went beyond the ridiculous by including decisions from Roy (no relation to Heather Roy) granting those very Labour MPs the call to speak in the debate - a perverse case of deliberately biting the hand that feeds.
Those MPs no doubt thought this was all terribly clever. They should watch the replays on Parliament TV. They looked juvenile. Worse, their behaviour would have confirmed everything the public thinks is wrong with Parliament.
Eric Roy's patience eventually ran out and he warned Labour to stop trifling with the chair.
From that point, things got confused as Mallard was told to leave the chamber but somehow remained, and proper debate finally started.
Labour's obstructive behaviour seemed to flow in part from it being miffed at being outflanked by Heather Roy.
Much of Labour's filibustering has been on the bill which has precedence on Parliament's order paper ahead of her measure.
That bill deals with the workings of the Royal Society of New Zealand, an academic body devoted to the promotion of science. Under normal circumstances, Parliament would have dealt with it in minutes - not months.
It is a further black mark on Labour that not only has an innocent third party been caught in the crossfire, but the presence of the Royal Society's measure on the order paper has been exploited for purely political motives.
Heather Roy caught Labour napping by moving the House report progress on the Royal Society of New Zealand Bill and move on to debating her measure.
The National-Act majority duly ensured this happened.
Labour justifiably questioned the use of something which is normally a procedural device to curtail debate. Lockwood Smith agreed it was something Parliament's standing orders committee should examine.
But he ruled that the vote on the motion should stand for the time being. From then, things quickly went downhill.
The Greens should likewise hold their heads in shame over being party to Labour's shoddy behaviour. They put much stock in parliamentary probity. Their only defence for voting in favour of Labour's dubious motions was that Keith Locke, the sole Green MP in the House at the time, seemed distracted.
Some of the Labour MPs caught up in this episode must now surely regret it.
One such MP, Wellington Central's Grant Robertson, felt obliged to post a lengthy explanation on Red Alert, the Labour MPs' blog.
He made no apology for the ways in which Labour was trying to stop Roy's bill. He admitted it was "unedifying" - surely the understatement of the week - but claimed it was all part and parcel of parliamentary practice.
Well, no. A clear line can be drawn between trying to delay a measure's progress through Parliament by filibuster and trying to find and exploit gaps, loopholes and apparent anomalies in Parliament's rules to subvert the will of the majority. Labour crossed that line.
On top of that, Labour's filibustering has denied other parties' MPs the opportunity to get their own private member's bills - some of which are worthy measures deserving of enactment - on to the order paper.
That is unfair. But it is symptomatic of Labour's lingering arrogance from its years in power.
Incredibly, it continues to try to pull the wool over voters' eyes by promising to bring in private member's bills to block things such as National's plans for partial state asset sales. Such talk is poppycock. Such bills would first have to be lucky enough to be drawn in the ballot which determines which bills get on to the order paper.
In the last ballot, 24 bills were vying for a lone spot.
Furthermore, there has not been a ballot since November last year. No prizes for guessing who is responsible for that.
