26 CFR §301.7272-1

1. (a)Any person who fails to register with the district director as required by the Code or by regulations issued thereunder shall be liable to a penalty of $50 except that on and after September 3, 1958, this section shall not apply to persons required to register under subtitle E of the Code, or persons engaging in a trade or business on which a special tax is imposed by such subtitle.
2. (b)For provisions relating to registration under sections 4101, 4412, 4455, 4722, 4753, and 4804(d), see the regulations relating to the particular tax. For regulations under section 7011, see § 301.7011-1.