I have been employed by an organisation from Feb 16 on a casual basis. As a casual employee, I am obliged to submit for approval a timesheet weekly on a Monday. On 29 Apr 16 a letter of offer, for a full-time position, was communicated to me. The organisation dated the commencement of that role as 26 Apr 16. As there was no time limit for consideration, I took the weekend to mull over the offer. On 2 May 16, I signed and returned the letter of offer. This to my mind constitutes as an employment contract that commenced on 2 May 16. 02 May was also the date that should I wish to be paid for works undertaken the previous week that I was required to submit a claim for payment. Today 04 May 16, the organisation claims that I must repay them monies paid to me for work I completed as a casual as I was not entitled to receive these funds. I would argue that I did not become party to any contract with the organisation until the date I consented to the terms of the offer and I am entitled to the payment received and should not be forced to re-pay the wages. My questions are, when did the employment contract come into existence, the date within the offer, the date of the communication of the offer or the date the offer was accepted? Am I obliged to repay the wages?