Registered charities can issue official donation receipts (also referred to as "tax receipts") to acknowledge gifts. An official donation receipt is subject to particular requirements under the Income Tax Regulations including identification that it is an official receipt for income tax purposes.
Note that registered charities issue other forms of receipts to acknowledge acceptance of services or items that are not gifts. These are not tax receipts and should be clearly distinguished from the tax receipts issued to acknowledge gifts. Contributions of services, that is, of time, skills or efforts, are not property and, therefore, do not qualify as gifts for purposes of issuing official donation receipts. Accordingly, a charity cannot issue an official donation receipt for services rendered free of charge.
(CRA : Charities Glossary)