If an electronic agreement is used (e.g. B an email), you must have appropriate computer system controls in place to ensure the security and accuracy of the agreement. To find out how much to withhold, deduct the Goods and Services Tax (GST) levied in the voluntary agreement from the amount of the invoice to be paid and multiply the result by the withholding tax rate specified in the voluntary agreement. However, if the recipient is registered for GST, the recipient may claim GST credits for all GST credits paid for items that the recipient purchases and uses to perform the work under the voluntary agreement. You do not need to send us a copy of the voluntary agreement, but you and the employee should each keep a copy for your records for five years after the last payment under the agreement.