No problem for employees.
This rule is for Employer.
That is ..imagine I am a partner in a Rent a car company with a Sponsor, I cannot start another rent a car company with another sponsor without permission from first sponsor.

So this rule is for Employer not employee...that is ...it is not for u..you can join anywhere...
Its like a pilot of Oman air can resign and join Kuwait Airways...after all he is a pilot..he cannot drive a truck..to avoid competition :)