I think you might have a case to take to NCAT under section 158 (below). Firstly, though, I would approach the EC member and tell them that you feel they have given themselves an unfair advantage with this by-law but that you are prepared to accept a new by-law where they pay their fair share for electricity etc.
Howvever, if they refuse you will take them to NCAT and seek back-payment of all the money they should have been paying for the past few years.
This is what section 158 says:
158 Order with respect to by-laws conferring exclusive rights or privileges over common property
(1) An Adjudicator may make an order prescribing the making, amendment or repeal, in terms of the order, of a by-law if the Adjudicator finds:
(a) on application made by an owner, that the owners corporation has unreasonably refused to make a by-law of the kind referred to in section 51, or
(b) on application made by an owner or owners corporation, that an owner of a lot, or the lessor of a leasehold strata scheme, has unreasonably refused to consent to the terms of a proposed by-law of that kind, or to the proposed amendment or repeal of such a by-law, or
(c) on application made by any interested person, that the conditions of such a by-law relating to the maintenance or upkeep of any common property are unjust.
(2) In considering whether to make an order under this section, an Adjudicator must have regard to:
(a) the interests of all owners in the use and enjoyment of their lots and common property, and
(b) the rights and reasonable expectations of any owner deriving or anticipating a benefit under a by-law of the kind referred to in section 51.
(3) An Adjudicator must not determine an application referred to in subsection (1) (a) by an order prescribing the making of a by-law in terms to which the applicant or, in the case of a leasehold strata scheme, the lessor of the scheme is not prepared to consent.
(4) For the purposes of subsection (1), an Adjudicator may determine that an owner has unreasonably refused consent even though the owner already has the exclusive use or privileges that are the subject of the proposed by-law.
(5) An order under this section, when recorded under section 209, has effect as if its terms were a by-law (but subject to any relevant order of a superior court).