BRUSSELS — European Union investigators searched the offices of the German automakers Daimler and Volkswagen on Monday — the second such action in recent days as part of an inquiry into allegations of illegal collusion by the country’s car giants.

Regulators are looking into whether Germany’s three major vehicle manufacturers — BMW, Daimler and Volkswagen — worked together to fix the prices of various vehicle equipment, including design aspects that help control emissions. The searches came as the companies face a backlash over their efforts to evade rules on diesel emissions.

The European Commission, the European Union’s executive arm, said in a brief statement that the “inspections” were aimed at enforcing rules that “prohibit cartels and restrictive business practices.” The commission did not name the companies involved, but Daimler and Volkswagen said their offices had been searched.

As in the enforcement action against BMW last week, the commission said the inspections, which also involved German antitrust officials, were a preliminary step in the investigation.