The National Association of Pension Funds (NAPF) commented on implications for the private sector.
James Walsh, NAPF senior policy adviser, said: "This ruling means that pension funds in the private sector are not left with further uncertainty around any move to CPI.
"Pension funds already face a complex task in deciding what the rules around switching from RPI to CPI mean for them, and this case could have added more uncertainty.
"Shifting to CPI can give a pension fund some much-needed flexibility, but there are implications for both current and future pensioners. Trustees and employers know that any switch must be handled carefully.
"One in four private sector final salary pensions is able to move from RPI to CPI. Many schemes have RPI 'hardwired' into their pension scheme rules."
TUC general secretary Brendan Barber said: "This is a disappointing judgement for pensioners and scheme members whether they draw a private, public or state second pension.
"But we take great heart that the court accepted the argument that the government did this to cut the deficit rather than carry out a proper consideration of the best way of measuring the cost of living for pensioners, even if only one judge said that it was unlawful.
"With the Office for Budget Responsibility now predicting that the long-term gap between CPI and RPI will be 1.4%, pensioners in both private and public sector schemes will find that their pensions will be 20p in the pound lower after 18 years of retirement.
"Ministers keep saying that they are cutting public sector pensions for the benefit of private sector workers, but this move hits both, as well as those with a SERPS or state second pension."
