(a) (1) In the case of any taxpayer whose federal adjusted gross income for the taxable year exceeds the threshold amount, each credit to which this section applies shall be reduced by six dollars ($6) for each two thousand five hundred dollars ($2,500), or fraction thereof, by which the taxpayer’s federal adjusted gross income exceeds the threshold amount.

(2) In the case of credit allowed by subdivision (b) of Section 17054 (relating to joint returns and surviving spouses), the “six dollars ($6)” referred to in paragraph (1) shall be applied by substituting “twelve dollars ($12).”

(3) In the case of a married individual filing a separate return, the “two thousand five hundred dollars ($2,500)” referred to in paragraph (1) shall be applied by substituting “one thousand two hundred fifty dollars ($1,250).”

(4) Under no circumstances shall any credit reduced by paragraph (1) be reduced below zero.