Union organizers at a hospital wanted to distribute leaflets to potential union members, but hospital rules prohibited leafleting in areas of patient care, hallways, cafeterias, and any areas open to the public. The National Labor Relations Board (NLRB), a government agency, ruled that these restrictions violated the law and ordered the hospital to permit the activities in the cafeteria and coffee shop. What kind of law was NLRB creating?
(a) A statute
(b) Common law
(c) A constitutional amendment
(d) Administrative regulation