A tax receipt is actually not obligatory. A charity may choose not to issue receipts because of the administrative burden, or it may elect to set a threshold policy dictating that only donations above a certain cash value will be issued a tax receipt. While it is not the law that charities must issue tax receipts, remember that donors can only claim their charitable tax credit if an official tax receipt is issued. So consider your donors when setting this policy – weigh the administrative burden against the value they place on their tax credit.
Visit this page on the Canada Revenue Agency website for more information.