A federal judge on Tuesday blocked JetBlue Airways from acquiring Spirit Airlines, agreeing with the Justice Department that the $3.8 billion deal would eliminate a competitor important to price-conscious travelers. 

The Justice Department said JetBlue’s purchase of Spirit would remove an ultra-low-cost carrier that benefits travelers and puts pressure on other airlines to keep down fares. Removing Spirit as a rival would free JetBlue to raise prices by as much as 30%, the government said. JetBlue is the country’s sixth-largest carrier, and Spirit ranks seventh.