It's not forcibly; a company is a group of people that sign a special type on contract (often called memorandum of association and bye-laws but other terms exist.)

That contract can govern all manner of different circumstances including the circumstances in which the allocation of shares are transferred.

Sometimes only a motion of the board is required, sometimes additionally a motion by a general meeting with various options for requiring super majorities across and within the different classes can be required too.

Fiduciary duties often require the Board to act in the objective best interest of the members.

In my opinion it is better model to think of a company as a club (hence shareholders often being called a Member) rather than something that you own.