29The applicants invoke the case-law of the European Union according to which acquired rights cannot, in principle, be called into question. They submit that the increase in the retirement age to 63 infringes Article 27(2) of the Statute for Members (see paragraph 8 above). They take the view that they acquired the right to an additional pension prior to 1 April 2009. Such a right arose, in their view, when they had paid contributions for the minimum period and it is thus in accordance with the rules for payment as set out in the provisions of the Rules of 12 June 1990 in force at that time that the detailed rules for enjoyment of that right ought to be determined. At the stage of the reply, they add that, in accordance with the judgment of 18 October 2011 in Case T-439/09Purvis v Parliament [2011] ECR II-7231, the decision of 1 April 2009 does not apply to the eight applicants who ceased to hold office as Members prior to 2009, since they had already acquired their right to the pension at the time when they ceased to hold office.