Killersaves,
It is entirely on your employer as to how your engagement with another firm as a partner, though a mere sleeping one, is treated. There are certain clauses in most of the laws that direct towards avoidance of dual employment.
1. Factories Act Section 60 pronounces Restriction on dual employment
Even regard to establishments which are not coming under the definition of factories act, some the provisions mentioned here-under would help for preventing double employment:
a. The Bombay Shops & Establishments Act, 1961.
Sec 65: Restriction of double employment on a holiday or during leave
No employee shall work in any establishment, nor shall any employee knowingly permit an employee to work in any establishment, on a day on which the employee is given holiday or is on leave in accordance with provisions of this Act.
Similar provision should be there in the respective states shops and establishment act.
b. Industrial Employment (standing Orders) Act,1946
In terms of model standing orders number 8 under schedule IA of central rules “ A workman shall not at any time work against the interest of industrial establishment in which he is employed and shall not take any employment in addition to his job in the establishment, which may adversely affect the interest of his employer.
Even if everything mention above is negated, every employer draft text of employment contracts and if required bring interpretations to suit them, to deter the employee from any gainful activity and activities that shall consume his/her time attention i.e an employee not covered under the Shops & Establishment Act and the Industrial Dispute Act is governed by the Contract of Service, which, in most cases, is the Appointment Letter.
So, I would suggest not traversing that path. However, my learned friends would be able to correct me and throw more light on the very matter discussed by you.