Too many facts to give definite answer. Here, are my general comments & questions re issues for now:
1. In Arizona not independent contractor (regardless what contract says) unless you have other clients -that is you have your own business like a plumber or a lawyer. Do you have your own business? If not you can set off a "nuclear bomb" on your employer.
2. Obvious a breach of contract. If the amount is under $2500 you can sue self in Justice court (Justice of the Peace nearest Defendant) and no attorney will be allowed (Small Claims Court). (They furnish form and filing fee is about $50. and can service by certified mail.)
3. If more than $2,500 but under $10,000 you can still sue by yourself in Justice Court but co can hire lawyer and rules of procedure and evidence will apply. This can be a killer but (A) lawyer fees may cost co more than claim, so incentive is for them to settle and (B) we can advise you behind scenes and (C) some AZ Justice court will grant attorneys fees to you even tho law firm not appear but only advise.
4. Need to be careful about notifying Costco and Sam's but I think they would want to know. Superior Court cases (if more than $10,000) are public record so disclosure of suit and claims would happen anyway - not true of Justice court cases. If contact, stick to facts, what you can prove -no "bad mouthing, etc."
Overall, the nuisance value of your claim may get it paid. and if you are really an employee (not a contractor) because no other clients -do not have own fed employer id #, etc. then your claim will be for triple damages under AZ law, not to mention 941 payroll taxes not paid which is complaint to AZ Industrial Commission and/or IRS.
Good luck.
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