The criteria for a large proprietary company are any two of the following: 50 or more employees, assets of $12.5 million or more and revenues of $25 million or more.
This includes changes to its members, changes to share structure, changes to directors and secretaries, and if there is a change to the ultimate holding company of a proprietary company.
While not a legal requirement, having employees sign non-disclosure agreements and conflict of interest statements helps to protect your trade secrets and proprietary company information.