You are not eligible for unemployment if you leave "without good cause". You have good cause if your employer makes a substantial change in the terms of your employment. If your boss is changing the percentage you earn on commissions, you would have good cause to quit and I believe you would be given unemployment benefits.
Adjustments down in pay can often provide valid grounds for an employee to leave their job and still collect unemployment benefits. Luckily, the Unemployment Website provides a listing of prior cases that you can compare yours to in order to determine if you are likely to qualify for benefits if you quit.
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