Synopsis As Introduced Amends the Illinois Income Tax Act. Creates an addition modification in an amount equal to the deduction for qualified domestic production activities allowed under Section 199 of the Internal Revenue Code for the taxable year. Makes changes concerning the definition of "unitary business group". Provides that no penalty shall apply with respect to an underpayment of estimated tax for the first, second, or third quarter of any taxable year ending on or after December 31, 2015 and ending prior to December 31, 2016 if (i) the underpayment was due to the changes made by the amendatory Act, (ii) the payment was otherwise timely made, and (iii) the balance due is included with the taxpayer's estimated tax payment for the fourth quarter. Effective immediately.