My work is substantially increasing my responsibility. They refuse to pay any increase in wage “until profitability improves.” How do owners get away with skimming off the top in good times and punishing workers in the bad?

I'm fuming about this. I have a stressful job and was just informed that my workload would substantially be increasing, with no raises or even cost of living adjustments. I'll even have to do sales- without commission! Anyone else experience this? What did you do?