Please reer to Section 21A of Trade Union Act :-
[21A. Disqualifications of office-bearers of Trade Unions.—(1) A person shall be disqualified for being chosen as, and for being member of the executive or any other office-bearer of a registered Trade Union if—
(i) he has not attained the age of eighteen years;
(ii) he has been convicted by a Court in India of any offence involving moral turpitude and sentenced to imprisonment, unless a period of five years has elapsed since his release.
(2) Any member of the executive or other office-bearer of a registered Trade Union who, before the commencement of the Indian Trade Unions (Amendment) Act, 1964, has been convicted of any offence involving moral turpitude and sentenced to imprisonment, shall on the date of such commencement cease to be such member or office-bearer unless a period of five years has elapsed since his release before that date.]
2[(3) In its application to the State of Jammu and Kashmir, reference in sub-section (2) to the commencement of the Indian Trade Unions (Amendment) Act, 1964, shall be construed as reference to the commencement of this Act in the said State.]
All members of Trade Union need not be employed by one employer. Read section 22:-
[22. Proportion of office-bearers to be connected with the industry.—(1) Not less than one-half of the total number of the office-bearers of every registered Trade Union in an unrecognised sector shall be persons actually engaged or employed in an industry with which the Trade Union is connected:
Provided that the appropriate Government may, by special or general order, declare that the provisions of this section shall not apply to any Trade Union or class of Trade Unions specified in the order.
Explanation.—For the purposes of this section, “unorganised sector” means any sector which the appropriate Government may, by notification in the Official Gazette, specify.
(2) Save as otherwise provided in sub-section (1), all office-bearers of a registered Trade Union, except not more than one-third of the total number of the office-bearers or five, whichever is less, shall be persons acutally engaged or employed in the establishment or industry with which the Trade Union is connected.
Explanation.—For the purposes of this sub-section, an employee who has retired or has been retrenched shall not be construed as outsider for the purpose of holding an office in a Trade Union.
(3) No member of the Council of Ministers or a person holding an office of profit (not being an engagement or employment in an establishment or industry with which the Trade Union is connected), in the Union or a State, shall be a member of the executive or other office-bearer of a registered Trade Union.]