Section 99. The commissioner may summon said licensees, companies or associations, or any of their agents or employees, and such other witnesses as he deems necessary, and examine them relative to their transactions and to the condition of their business, and for that purpose may administer oaths. Whoever without justifiable cause refuses to appear and testify 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 five hundred dollars or by imprisonment for not more than six months, or both.