Section 24F. The commissioner, or such other of his assistants as he may designate, may summon a licensee, or any of his agents or employees, and other witnesses as he considers necessary, and examine them relative to their transactions, may require the production of books and papers and, for those purposes may administer oaths. Whoever, without justifiable cause, fails or refuses to appear and testify or to produce books and papers when so required, or obstructs the commissioner or his representatives in the performance of their duties, shall be punished by a fine of not more than $500 or by imprisonment for not more than 6 months, or both. Each day a violation occurs or continues shall be considered a separate offense.