European Union antitrust regulators have opened an extensive investigation into USA office supplier Staples’ $6.3 billion bid for rival Office Depot as they warned about possible price hikes as a result of the deal.

The European Commission said on Friday that the deal could hurt business customers with global contracts in Europe and those with national contracts in the Netherlands and Sweden.

Now the European Commission has expressed concerns, saying its initial investigation had shown that the tie-up could eliminate competition and “reduce the choice of suitable suppliers in already concentrated markets”.

“Several smaller players have a more limited geographic presence and may not be able to exercise a sufficient competitive constraint on the merged company”, the commission said.

Staples and Office Depot, together with Lyreco, are the main suppliers of office products to business customers.

“All companies and organizations, big or small, need office supplies for their daily work”, EU Competition Commissioner Margrethe Vestager said in the statement on Friday. European Commission’s Phase II is an in-depth analysis of the merger’s effects on competition.

If the office-supply retailers combine, Sargent has said the headquarters will be at Staples’ home of Framingham, Mass. Office Depot employs about 2,000 people at its Boca Raton headquarters.

Authorities in the United States and Canada continue to weigh the merger.

The company is looking at the acquisition as a way for it to compete better against Wal-Mart and Amazon, its new rivals in selling paper, pens and ink cartridges.

The deal, announced in February, would take the US down to one chain of office-supply superstores from three in just a couple of years, after USA regulators approved Office Depot’s acquisition of OfficeMax in 2013.

The transaction was notified to the Commission on August 21, 2015.