Under the Securities Exchange Act of 1934, a private Shareholder who Owns an amount of Shares meeting/exceeding 5% of the Total Outstanding (but not greater than 20%), must File an SEC Schedule 13G Form/Report, provided the private Shareholder is a passive Investor and does not plan on exerting Control.
If the size/quantity of the Shareholder's stake exceeds 20%, then the Shareholder must File an SEC Schedule 13D Form/Report.