JetBlue Airways Corp. agreed to transfer some Spirit Airlines Inc. gates and flight slots at three airports to help lessen antitrust concerns over its pending acquisition of the low-cost carrier.

JetBlue will shift all of Spirit’s holdings at Boston Logan International and Newark Liberty International and part of its assets at Fort Lauderdale-Hollywood International in Florida to Allegiant Travel Co., according to a statement Monday. JetBlue previously agreed to divest Spirit’s holdings at New York’s LaGuardia Airport to deep discounter Frontier Group Holdings Inc.

The US Justice Department is trying to break up the JetBlue-Spirit deal on grounds it would give the combined company too much market power in certain areas and lead to higher fares for consumers. A trial is scheduled for October. JetBlue says the acquisition is necessary for it to compete with larger carriers that control more than 80% of the US commercial airline market.

JetBlue rose 1% at 9:42 a.m. in New York, and Allegiant gained 2%. Spirit was little changed.

The divestitures are subject to approval by local airport authorities, the Federal Aviation Administration and the US Transportation Department and will only occur after the JetBlue-Spirit transaction closes.