Manifest arbitrariness: delegated rules lacking rational foundation can be invalidated for being ultra vires and unreasonable. Manifest arbitrariness describes action or subordinate legislation that is unreasonable, capricious, or dependent on will alone and thus non-rational; such conduct fails the test of reasonableness underlying the equality guarantee. Delegated legislation is subject to invalidation only when it is so lacking in rational foundation that it could not reasonably be expected to emanate from the delegated authority, rendering it ultra vires or contrary to equality.