the rule

A common statement is which a person attempts to convey that "rules" (policies, laws, etc) must be followed irrespective of personal intuition or any sense of what really makes sense. "Rules is rules" conveys that it is the rule, and nothing else, that determines a certain action or inaction. The statement is usually used in a context where it is believed that the rule "doesn't make sense", but it must be followed anyway, simply because it is a rule.