A
"trade union" is any temporary or permanent combination (whether or not
registered as an industrial organisation under this Act)--
(a) for regulating the relations between--(i) employees and employers, or(ii) employees and employees, or(iii) employers and employers, or
(b) for imposing restrictive conditions on the conduct of any trade or business,whether or not such a combination would, except for this Act, be an unlawful combination because one or more of its purposes is in restraint of trade.