An SEC regulation that requires tender offers to be available to all holders of the identical class of the security.

For example, if company ABC has tendered an offer to buy back its B shares, then all holders of this class must be allowed to participate in the buy back. The SEC does not require ABC co. to offer this buy back to the shareholders of its other classes.

This rule is especially important during takeover bids, ensuring that any tender offers made by the acquiring company cannot be directed only to those shareholders in favor of the takeover.