A federal judge on Tuesday blocked JetBlue Airways’ proposed $3.8 billion acquisition of Spirit Airlines, a victory for the Department of Justice, which argued that the deal would harm travelers.

In his ruling, Judge William G. Young of the U.S. District Court for the District of Massachusetts sided with the Justice Department in determining that the merger would reduce competition in the airline business.

The proposed merger would have created the nation’s fifth largest airline. The Justice Department had argued that smaller, low-cost airlines like Spirit help keep fares low and that allowing the company to be acquired by JetBlue, which tends to charge higher prices, would have hurt consumers.

This is a developing story. Check back for updates.