The amount of any penalty under section
6694
(a), section 6695, or 6695A shall be assessed within 3 years after the return or claim for refund with respect to which the penalty is assessed was filed, and no proceeding in court without assessment for the collection of such tax shall be begun after the expiration of such period. In the case of any penalty under section
6694
(b), the penalty may be assessed, or a proceeding in court for the collection of the penalty may be begun without assessment, at any time.