That is actually true on occasions in Australia. With high marginal tax rates, many refuse overtime (aka known as a salary increase) if that OT would force them into a higher tax bracket. Depending upon the situation the extra OT could cause the tax to be greater than the extra pay gained.
Don't haven't all the time but the phenonium is well enough known.
I worked at the Argyle diamond mine, (which is reputedly in Australia but is as close to being nowhere of anywhere that I have been), and I heard this same thing from some of the electricians working construction there. This is not very likely. It says that Australia doesn't have marginal tax rates, that they tax the entire earnings at the higher rate as your income goes up or that they penalize overtime pay by essentially taking it all away. Neither would make any sense.
I also heard the same thing from construction workers in the US and Canada. I am familiar enough with the taxation in both of those countries to know that it is not true.
I managed construction in heavy industrial installations for most of my career. We don't want to pay overtime. It is paying more and getting lower productivity and increased safety concerns in return, because the workers are tired. It is a headache to fairly distribute the overtime so that all of the workers receive a share. They deny it but some crews will slow down their work in the normal forty hour work week to force more overtime work once you start to use overtime too frequently.
But sometimes it is unavoidable. Late deliveries of equipment and materials, bad weather, equipment breakdowns, last minute engineering changes, all can force overtime. It is much better to plan to mitigate the need for overtime by staffing up and by running night shifts to clean up the problems that pop up before they become serious. But you can only justify this on larger job sites.
I know, TMI and further derail.