Leading tyre manufacturers Pirelli (PIRC.MI), Continental (CONG.DE), Michelin (MICP.PA), and Nokian Tyres were raided by EU antitrust regulators on Tuesday as part of an investigation into a possible cartel, sending their shares down.

The European Commission, which acts as competition enforcer in the 27-country European Union, said it had raided several tyre makers in several EU countries. It did not provide further details, in line with its policy on such matters.

Italian company Pirelli told Reuters it had acted fairly and “always in total compliance with all rules and regulations”.

“Pirelli informs that it is guaranteeing full support to the authority in the ongoing investigations,” a spokesman for the Milan-based company said.

German rival Continental confirmed that investigations by European antitrust authorities were taking place at the company’s offices in Germany.

France’s Michelin said it was included in the EU investigation and that it strictly complies with competition rules.

Nokian Tyres (TYRES.HE), meanwhile, said its headquarters in Finland were raided and that it was cooperating with the EU authority.

Pirelli shares were down as much as 3.8% before being briefly suspended from trading. Michelin fell 2.9% and Continental was down 3.5%.

The EU watchdog said products related to the inspections were new replacement tyres for passenger cars, vans, trucks and buses sold in the European Economic Area comprising EU countries, Norway, Iceland and Liechtenstein.

It said the raided companies may have breached EU rules against cartels.

“The Commission is concerned that price coordination took place amongst the inspected companies, including via public communications,” the EU executive said in a statement.

Companies found guilty of breaching EU antitrust rules face fines of as much as 10% of their global turnover.

In recent years the Commision has fined nearly a dozen cartels in the car industry, among them suppliers of automotive bearings, car seats, braking systems and even a cartel that restricted competition in emission cleaning for new diesel passenger cars.

Reporting by Foo Yun Chee Additional reporting by Giulio Piovaccari in Milan and Gilles Guillaume in Paris Editing by Mark Potter and David Goodman