The tentative agreement with the NetJets Association of Shared Aircraft Pilots, which represents 2,500 pilots, boosts pay and retirement benefits, and changes the compensation structure so that pilots who fly more are paid more. It expires in 2026.

NetJets and the union said in a joint statement on Thursday that the accord followed six weeks of talks, which the Columbus, Ohio-based company began though the pilots' 2015 contract wasn't scheduled to expire until 2023.

More than 81 percent of the pilots voted last month in favour of the changes.

"The NJASAP Executive Board is exceedingly pleased with the outcome of this negotiation -- an ambitious undertaking characterized by honesty, goodwill and a genuine commitment to continuing collaboration," said union president, Pedro Leroux.

NetJets specializes in "fractional" aircraft ownership, which lets individuals and companies buy shares of private jets and travel on short notice. Its U.S. fleet has about 450 planes.

The agreement was reported earlier by The Wall Street Journal.

NetJets' labour peace contrasts with more than two years of contentious relations with the union that ended in 2015, after Adam Johnson was installed as chief executive.

The union, then also led by Leroux, had accused NetJets of trying to slash jobs, obtain givebacks on healthcare and work rules, and bait pilots through bogus Twitter posts to conduct work slowdowns that could result in their being fired.

In contrast, Johnson said on Thursday the contract extension was "built on a foundation of trust and transparency."

Berkshire, based in Omaha, Nebraska, employed more than 377,000 people at the end of 2017, and most are not unionized.

Buffett, who flies on NetJets planes, told shareholders at Berkshire's 2015 annual meeting: "We have no anti-union agenda whatsoever, and we think we have sensational pilots."

(Reporting by Jonathan Stempel in New York; Editing by Bernadette Baum and Tom Brown)