An Italian consumer group is inviting car buyers to join a class action lawsuit against Fiat and Volkswagen over allegations that the companies exaggerated the fuel-saving credentials of their vehicles.

After conducting tests on Fiat’s Panda 1.2 and Volkswagen’s Golf 1.6 TDI models, Altroconsumo said on Tuesday the two models were between 18 and 50 percent less fuel efficient than stated by the two manufacturers in their marketing and sales material.