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You should carefully read the papers you received when you applied for welfare. They will state the considitions under which you are eligible for welfare (whatever type) & what to do if you become ineligible (employed.)
If you receive welfare assistance during a time that you are not qualified to do so, your assistance will be cut off and you can be prosecuted for a FELONY. Also, if you are prosecuted, you will not be able to receive assistance for a specific time in the future, depending on the offense and level.
If you believe that you are violating the rules on receiving welfare, you should terminate the receipt of same immediately. Review your paperwork & report to your welfare supervisor that you are working (or whatever other disqualification you believe exists.)