A preemptive right entitles an existing owner to participate in a new issuance in proportion to their current holding, so that their percentage is not reduced without their choice.

Not automatic. Most modern statutes make preemptive rights available only if the charter or operating agreement provides them. In closely held companies their absence is a standard route to dilution.

Mechanics that matter. Notice period; whether the price and terms must match those offered to the third party; whether unsubscribed shares may be taken up by participating holders; and exclusions for equity issued under employee plans, in acquisitions, or to lenders.

Anti-dilution provisions are different, and address price rather than percentage. Full ratchet resets the conversion price of preferred stock to the new lower price. Weighted average adjusts it partially, taking account of how much new stock was issued. Weighted average is the market standard; full ratchet appears in distressed rounds.

Pay-to-play provisions strip protections from investors who decline to participate in a down round, and are increasingly common.

For minority owners without either, a capital call priced below value is the classic squeeze. The defense is to negotiate participation rights at investment, because after the call is announced there is nothing to negotiate with.