WASHINGTON – The federal government wants to block a deal that would increase United Airlines' grip over Newark Liberty International Airport, saying that it would drive up fares.

Newark serves 35 million passengers a year, and its airfares are already among the highest in the nation.

The Justice Department on Tuesday sued to block a deal that would let United acquire 24 takeoff and landing slots at Newark from Delta Air Lines. Federal officials said the agreement would give United—already the dominant airline at the airport near Lower Manhattan—an even greater competitive advantage that would lead to higher fares and fewer choices for passengers.