I therefore propose responding to the referring Court as follows.
In determining the point in time at which a pension fund has taken prospective measures concerning periods of service that have taken place after the judgment of 17 May 1990 in Barber (C‑262/88, EU:C:1990:209), to enforce the principle of equal pay for equal work between men and women under Article 157 TFEU with respect to normal pension age, which is a question for the referring court to decide, due regard is to be afforded to the fact that, under the combined effects of Article 19(1), second subparagraph TEU, and Article 47 of the Charter of Fundamental Rights of the European Union, Member State law must ensure that equal treatment with respect to normal pension age is a binding obligation that is fully enforceable both in practice and in law, and that the legal remedies provided by Member State law to guarantee equal pay under Article 157 TFEU with respect to normal pension age do not render this right impossible in practice or excessively difficult to enforce. At the same time, the remedial scheme to secure equal treatment with respect to normal pension age must be the same as that applicable to analogous claims of a purely domestic nature.
During the period prior to this occurring, and in which the Barber window remains open, the prohibition under EU law on retroactive levelling down, which precludes imposition of a retirement age for women (the advantaged class) that is the same as that for men (the disadvantaged class), applies even when the rules of a pension scheme confer a power, as a matter of domestic law, upon the amendment of its Trust deed, to reduce retrospectively the value of both men’s and women’s accrued pension rights for a period between the date of a written announcement of intended changes to the scheme and the date when the Trust deed is actually amended.
33, 43-47, 53, 59, 66