There are two classes of broadcasting station licences, namely, those for Class A and Class B stations respectively. A broadcasting station licence continues in force for a period of five years, and is renewable annually thereafter. The A class stations receive proportions of the available revenue, which means the balance of the fees collected by the Department under the regulations, subject to certain deductions. The available revenue is payable quarterly, on dates to be determined by the Minister and to such extent as the Minister considers justified. In Victoria there were two A class stations - the two plaintiffs the Broadcasting Co. of Australia Pty. Ltd. and the Associated Radio Co. of Australia Ltd. - which were entitled to the available revenue in accordance with the regulations in the proportions of 70 and 30 per cent respectively. These companies, in May of 1928, sold and assigned to the third plaintiff, Dominion Broadcasting Pty. Ltd., as from 1st March 1928 and 1st January 1928 respectively, all licence fees and revenues received from their broadcasting operations. In August of 1928 the Governor-General made certain regulations (1928 No. 79) under the Wireless Telegraphy Act 1905-1919, one of which was as follows: - "3. (1) After regulation 67 of the Wireless Telegraphy Regulations the following regulation is inserted: - 67a. In addition to the amount deductable from the licence-fees specified in the last preceding regulation, the Postmaster-General may deduct from the respective licence-fees an amount not exceeding fivepence for each month of the currency, after 1st November 1927, of any such licence issued before 1st January 1928. Of the amount so deducted the sum of threepence shall be utilized by the Postmaster-General in accordance with clause 8 of the agreement contained in the Schedule to the Wireless Agreement Act of 1927, and the balance shall be utilized as the Postmaster-General thinks fit. (2) This regulation shall be deemed to have commenced on 1st November 1927."