The European Union plans to investigate whether there is anti-competitive behavior among e-commerce sites across the 28-nation bloc.

The investigation, which will last more than a year, will examine a number of online retailers and websites, including giants like Amazon, which accounts for a large chunk of Europe’s e-commerce.

Margrethe Vestager, the European Commission antitrust chief, says she wants to investigate why cross-border purchases make up only 15 percent of the EU’s online sales.

Ricardo Cardoso, a spokesperson with the European Commission, says the investigation is aimed at a broader goal. “There is an overarching ambition of the commission to make sure that we have a single market in online in general,” says Cardoso.