If there is nothing in the contract to that effect, I think you may be correct in saying that you can do the tax return – provided you are the elected treasurer.
Have a look at sections 23 and 24 of the Act (below) wich say nothing about tax returns but do define who can do what in regard to finances.
Also, ask your strata manager how much they plan to charge for organising their tax agent to do the returns. If it’s a small figure you may as well let it go.
(1) The functions of a treasurer of an owners corporation include the following:
(a) to notify owners of any contributions levied in accordance with this Act,
(b) to receive, acknowledge, bank and account for any money paid to the owners corporation,
(c) to prepare any certificate applied for under Division 4 of Part 5 of Chapter 3,
(d) to keep the accounting records and prepare the financial statements.
(2) The treasurer of an owners corporation may delegate the exercise of any of the treasurer’s functions (other than this power of delegation) to another member of the executive committee if:
(a) the delegation is specifically approved by the executive committee of the owners corporation, and
(b) the executive committee specifically approves of the function being delegated to that member of the executive committee, and
(c) the delegation is subject to such limitations as to time or otherwise as the executive committee requires.
(3) While a delegate is acting in accordance with the terms of such a delegation, the delegate is taken to be the treasurer of the owners corporation.
(4) The executive committee of an owners corporation may, by a notice in writing served on the treasurer of the owners corporation, order the treasurer not to exercise any of the treasurer’s functions that are specified in the notice unless the treasurer does so jointly with another person so specified.
A person must not exercise any of the functions of an owners corporation or the treasurer of an owners corporation relating to the receipt or expenditure of, or the accounting for, money of the owners corporation or the keeping of the books of account of the owners corporation unless the person is:
(a) a member of the owners corporation or of the executive committee and the treasurer of the owners corporation or of the executive committee, or
(b) a strata managing agent who is empowered to exercise that function, or
(c) a person with whom the treasurer of the owners corporation is required by an order of the executive committee to exercise that function jointly, and who is enabling the treasurer to comply with the order, or
(d) a member of CPA Australia, or a member of the Institute of Chartered Accountants in Australia, authorised by the owners corporation to exercise the function, or
(d1) a member of the Institute of Public Accountants authorised by the owners corporation to exercise the function, or
(e) during the initial period only—a person authorised by the original owner to exercise the function.
Maximum penalty: 5 penalty units.