Question: how much can you earn before paying secondary tax?
Answer: You pay an additional 12.50% in tax on $2,000 as over $48,000 you go into the next tax bracket. If you earn $50,000 per year from your main income and earn another $10,000 from a second job your extra income stays in the same tax bracket so the tax rate doesn't increase. You will find more details on the rates here.