You appear to have what can only be described and an autoctratic attitude towards dealing with staff. An attitude that would see turnover of staff for the simplest of mistakes.
I do hope that you are not in a position where you have the ability to dismiss staff.
When you take on staff whether you like them or not! as a business you are playing with people's livelihoods. To sack someone on the spot shows you absolute contempt for your fellow workers.
People react in different ways, for different reasons.
If a crew person has having issues with punctuality then I would take the time to find out WHY and may be HELP them get through their predicament if you can and they want help. Most people I know won't ask for help because of attitudes like yours ( for fear of retribution )
I bet if you took a friendly and concerned approach you would have a much better chance of addressing the situation and keeping an employee who may be very good.
If He/She's NO GOOD then you better look at your hiring procedures big time. The process allows full analysis of potential staff thru the interview and OJE staff.
May be temporary availability change, extended leave if necessary. what ever it takes with in you capability to help. Why would you risk losing valuable staff by having a blanket policy attitude ?
As for part time staff joining a union. If you and the rest of your business managers have your attitude towards discipline then can you really blame them for asking for protection from a union.
A bet that staff who protest are not against the business but have been driven to that level of frustration by bosses who a not listening to staff, not concerned for their staff welfare and have your "sack'em now boy"!attitude to dealing with issues. Your staff will follow a goodleader not be beaten in to submission. Slavery went out ages ago!!
If there were better handling of staff issues then unions may not be needed.
McD's don't have a strong union following in NZ but people do have the freedom to join with out fear of reprisal. I think wer'e lucky that business owners in NZ appear to be more willing to listen in this country. We still have our fair share of arseholes as well.
Take a gooooooodddd look at what your beliefs are mate because the one you appear to have will prevent you from ever having a successful business of your own. You'll have the wporld record for the highest staff turnover. And as Gill indicated could end you up with your own named set in the employment tribunal office.
Damn one eyed, green-horned, fire breathing managers really piss me off. It's bloody well not necessary to be like that!!