"We are concerned that this may result in preferential treatment compared to those of competing services, which may be hurt as a consequence," Almunia said in a statement.
He also said Google might be copying content from rival travel and restaurant guides and that some of its agreements might restrict competition in online advertising.
Mistique Cano, a Google spokeswoman, said the company has "only just started to look through the commission’s arguments."
"We disagree with the conclusions but we're happy to discuss any concerns they might have," she said. "Competition on the Web has increased dramatically in the last two years since the commission started looking at this and the competitive pressures Google faces are tremendous. Innovation online has never been greater."
In his statement, Almunia said he hopes to resolve the dispute quickly.
"I believe that these fast-moving markets would particularly benefit from a quick resolution of the competition issues identified," he said.
The U.S. Federal Trade Commission is also investigating whether Google has violated antitrust laws, but the agency has not yet reached any formal conclusions.