(a) Notwithstanding any other provisions of this act to the contrary, no legal action for the collection of contributions, interest and penalties shall be instituted after the expiration of six years from the end of the calendar year determined in accordance with subsection (b) of this section, unless prior to the expiration of such six-year period and with respect thereto (1) an assessment proceeding shall have been instituted pursuant to the provisions of section three hundred four of this act, or (2) an action shall have been instituted pursuant to the provisions of section three hundred nine of this act, or (3) a lien shall have been entered pursuant to the provisions of section three hundred eight point one of this act: Provided, That the provisions of this section shall not apply where an employer by willful failure or refusal to file a report with the department or to include in any report all wages which he has paid, or otherwise, has attempted to avoid or reduce liability for the payment of contributions.

(b) The calendar year referenced in subsection (a) of this section shall be the later of the following calendar years: (1) the calendar year in which the wages were paid with respect to which liability for the payment of contributions, interest or penalties, as the case may be, is based, or (2) with respect to contributions, interest or penalties due on wages paid by a successor-in-interest after a transfer of organization, trade, business or work force, in whole or in part, from a preceding employer, the calendar year in which the successor-in-interest files the report required by section 315(a)(2)¹ of this act in accordance with section 315(b) of this act.