Notwithstanding any other provision of this act, all employers required to pay contributions under section 301 or 301.1,¹ except those subject to the provisions of section 301(a)(3) and (4) or 301.1(g), shall pay additional contributions at a rate of zero per centum (0.0%) for calendar year 1989 and at a rate as set forth in section 301.7 for each calendar year thereafter on wages paid with regard to the limitation specified under section 4(x)(1) of this act.²