BRUSSELS — A top European Union legal adviser said Thursday that software installed in Volkswagen cars to alter the amount of pollutants coming out of their exhaust pipes in hot or cold weather and at high altitude doesn’t conform to the 27-nation bloc’s laws.

The case arose when Austrian courts asked the European Court of Justice to rule on whether the software made by Volkswagen, which also includes Porsche, constitutes a “defeat device” that could be used to cheat on car emissions tests.

The legal opinion by Advocate General Athanasios Rantos, which also said that the software cannot be justified as a way to protect car engines, is not binding on the ECJ, but Europe’s top court does follow such advice in most cases.