Three sources told Reuters about the de facto new policy, which they say is meant to stop a recent rally fizzling out.
Chinese regulations define a "major shareholder" as one with a stake of 5% or more.
Rules say they are required to make a public filing with the relevant stock exchange before selling shares.
But sources told Reuters the Beijing exchange has been rejecting such filings.
They added it was not clear how long this new policy would remain in place.
The Beijing exchange and the China Securities Regulatory Commission did not immediately reply to requests for comment.
The bourse was launched two years ago, aiming to drive funding for innovative small companies, nicknamed 'little giants'.
But investors had largely shown a lack of interest, until this month.
The market's benchmark 50 Index surged 46% in November due to recent measures by authorities intended to make it easier to invest there.
The Beijing bourse currently houses 232 listed companies with a combined market capitalisation of some $50 billion.
That's a small fraction of the value of firms listed on the Shanghai stock exchange.
