United Airlines will offer all lie-flat premium seats on its flights between Boston and San Francisco from June, as competition grows for business passengers on transcontinental routes.

The Chicago-based carrier will switch to Boeing 757-200 and Boeing 777-200 aircraft from a mix of Boeing 737-900ERs, 757-300s and 777-200s on the route on 8 June, FlightGlobal schedules show. The aircraft types remain unchanged through the end of 2017.

The 757s operating on Boston-San Francisco are either international aircraft with 16 lie-flat first class seats or domestic premium service (PS) aircraft with 28 lie-flat first class seats, the schedules show. All of United's domestic 777s have 28 lie-flat first class seats.

A United spokesman declines to comment on whether there will be any changes to the inflight service on the route.

"We're always looking at the markets that we're serving and the aircraft we're flying to make sure they're a right fit," he says on the aircraft changes.

United offers an improved PS inflight service on flights between Newark and both Los Angeles and San Francisco.

US carriers are increasingly battling for transcontinental premium passengers with improved products and, in some cases, service. While previously limited to just the New York to Los Angeles and San Francisco routes, JetBlue Airways has expanded its own premium product Mint to routes from Boston and Fort Lauderdale since 2016, placing pressure on competitors in those markets.

JetBlue operates Mint, which is flown on Airbus A321s with 16 lie-flat seats and a premium service, to both Los Angeles and San Francisco from Boston.

Delta Air Lines also operates 757-200s with a lie-flat premium product onboard between Boston and San Francisco, FlightGlobal schedules show. It began offering free meals in economy on the flights earlier in April.

This is not the first time United has flown an aircraft with lie-flat premium seats to Boston. It operated a 757 with lie-flat first class on the Boston-Los Angeles route during the summer of 2015 and has since flown one on the Boston-San Francisco route.

The carrier's Boston-Los Angeles flights continue to be operated with a standard domestic 737-900ER, the schedules show.

United's daily seat capacity will decrease by about 3% following the switch to lie-flat premium class aircraft between Boston and San Francisco, schedules show.

Source: Cirium Dashboard