Section 676. Employer's failure to withhold

If an employer fails to deduct
  and withhold tax as required, and thereafter the tax against which  such
  tax  may  be  credited  is  paid, the tax so required to be deducted and
  withheld shall not be collected from  the  employer,  but  the  employer
  shall  not  be  relieved  from liability for any penalties, interest, or
  additions to the tax otherwise applicable in respect of such failure  to
  deduct and withhold.