Critics say regulators need to crack down harder on automakers for gaming emissions tests. In this photo, a Greenpeace activist holds a banner during a protest in VW's home of Wolfsburg, Germany, Sept. 25, 2015. Reuters/Fabian Bimmer

Europe’s top environmental regulator raised concerns over automakers cheating emissions tests more than two years before the Volkswagen scandal broke, according to internal European Commission documents obtained by Financial Times.

Since VW admitted last month to gaming mandatory emissions tests in the United States and Europe, critics have brought renewed attention to the question of how regulators should control pollution from cars. The newly released documents show top-level European regulators were aware of manipulation on the part of automakers well before last month -- and struggled to formulate a response.

The Wolfsburg, Germany-based automaker has acknowledged it equipped 11 million of its diesel cars worldwide with software specifically designed to reduce emissions during tests -- a tool known as a “defeat device.”

In February 2013, Janez Potocnik, then European environmental commissioner wrote a letter to Antonio Tajani, the commissioner in charge of industrial policy. Potocnik expressed unease over the EU’s testing regime and the apparent struggle of regulators to enforce auto emissions standards, noting the “significant discrepancy between the certified emissions and those actually observed on the road.”

“There are widespread concerns that performance has been tailored tightly to compliance with the test cycle in disregard of the dramatic increase in emissions outside that narrow scope,” the environment commissioner wrote. “Vehicles are required to comply with the Euro limit values in normal driving conditions, and my services and I are often put in an uncomfortable position when defending the perceived lack of action by the commission and member states in addressing the obvious failure to ensure this.”

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Potocnik then urged Tajani to consider tough measures to crack down on the automakers like withdrawing emissions approvals for model lines and requiring “remedial action” from companies.

According to people familiar with the subject who were interviewed by Financial Times, concerns did not stem from the use of “defeat devices” but rather from legal techniques used to inflate testing results.

The exchange between Potocnik and Tajani, FT reports, was prompted by a separate letter that both men received a month earlier from Denmark’s environmental minister complaining about emissions testing procedures.

Since the scandal erupted, Volkswagen has replaced its CEO and suspended about 10 senior executives. This month, the company announced it would recall 8.5 million of its rigged diesel vehicles in Europe.