Is it illegal to pay under the table for a few hours?

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I want to start up a food cart business. I would only need someone to help me prepare and sell food for a few hours a day and for maybe 3 days a week at most. it's a slow start while i keep my full time job and want to see if this idea can become something good where i can eventually leave my job and run my business. I know i will be dealing with licenses and permits and the paper work that goes with opening a business and it would help a lot if i could skip payroll paperwork while I'm just feeling out this idea and only having someone help me for a few hours. Thank you for any tips and advice.

Is it illegal to pay under the table for a few hours?