Years ago when I was completing my apprenticeship, I asked for a raise when I became a Tradesmen.
My boss informed me that if I went up in hourly rate, then I would be crossing a tax threshold and would effectively earn less for the amount worked.;(because an increase in wage means higher expectations)
So, my young mind accepted that as fact and took minimum wage for my trade.
Years later and I'm now earning a fair chunk of change more and I can see how much of a lie that was.
Don't listen to your boss when they do something shitty like that, they don't have your best interest in mind, just theirs.