Where, by reason of the operation of subsection 112(3), the amount payable by an employer as an instalment of tax is greater than the instalment that would have been payable if it had been ascertained by reference to the employer's estimate, the Commissioner shall cause to be served on the employer a notice in writing specifying:
(a) the amount of the increase in the instalment of tax that became payable by reason of subsection 112(3); and
(b) a date as the due date for payment of that amount, being a date not less than 14 days after the date of service of the notice;
and the amount of the increase in the instalment of tax so specified is, notwithstanding section 103, due and payable on the date so specified.