The European Union is looking into a planned deal between Google and Yahoo.

“In mid-July, we decided to open a preliminary investigation on our own initiative into potential effects of the Google-Yahoo agreement on competition in the European Economic Area (EEA) market,” said Jonathan Todd, a spokesman for European Competition Commissioner Neelie Kroes.

Under terms of the deal, first announced in June, Google will supply Yahoo with advertising services to run alongside Yahoo’s own Web search system.

The probe is similar to one in Washington, where the U.S. Justice Department is also looking into whether a commercial tie-up between the two companies, which together have 80 percent of the market, would violate antitrust law.

Google and Yahoo said that they would cooperate with the Brussels probe.

“The agreement is limited in scope to Yahoo’s U.S. and Canadian websites, and it will not have any significant effect on Europe. We are, of course, cooperating with the commission and are confident that they will reach the same conclusion,” said Google spokesman Adam Kovacevich.

Companies ruled to be in breach of the EU’s competition rules can face fines of up to 10 percent of their global revenues.