By Jessica Sier

The European Commission has opened an in-depth investigation into whether the proposed merger between Fiat Chrysler Automobiles NV and Peugeot SA will reduce van competition in the European Economic Area, the Commission said on Wednesday.

The investigation will look at whether a merger between both companies, who have market-leading positions in many European countries, would disadvantage other producers of light commercial vehicles below 3.5 metric tons, or vans.

"We will carefully assess whether the proposed transaction would negatively affect competition in these markets and ensure that a healthy competitive landscape remains for all the individuals and businesses relying on commercial vans for their activities," said Margrethe Vestager, executive vice-president of the European Commission.

The Commission has 90 working days, until Oct. 22, to make a decision.

Neither Peugeot or Fiat Chrysler have submitted commitments to the initial investigation to address the preliminary concerns, said the Commission.

The European Commission has undertaken a preliminary investigation that shows Peugeot and Fiat Chrysler often compete head-to-head in the vans segment and have priced their vans accordingly.

The Commission is concerned a merger would remove an important competitive constraint for both of them and is looking primarily at markets in Belgium, Croatia, Czechia, France, Greece, Hungary, Italy, Lithuania, Luxembourg, Poland, Portugal, Slovakia, Slovenia, Spain and the U.K.

The van segment, or light vehicle below 3.5 tons, is characterized by high barriers to entry and expansion, said the Commission.

Write to Jessica Sier at jessica.sier@wsj.com