(Reuters) - NetJets, the luxury plane unit of billionaire Warren Buffett's Berkshire Hathaway Inc, has been sued by its 3,000-member pilots union for allegedly interfering with its communications with aircraft owners and customers about contract negotiations.

In a lawsuit filed on Monday, the NetJets Association of Shared Aircraft Pilots objected to a March 8 email from a senior NetJets executive. The email said it violated company policy for pilots to refer owners to a union website to learn about talks to amend their collective bargaining agreement.

The union said the email "necessarily implied" that pilots could be disciplined and even fired for mentioning the website, suppressing their speech and violating the federal Railway Labor Act governing airline labor relations.

NetJets did not immediately respond to requests for comment.

The lawsuit filed in the federal court in Columbus, Ohio, where NetJets is based, seeks an injunction protecting pilots from discipline for referring people to the union website or expressing support for the union.

NetJets and the union had years of contentious relations in the previous decade before agreeing to a contract in 2019.

Berkshire, based in Omaha, Nebraska, employed more than 382,000 people at the end of 2022. Most are not unionized.

Buffett flies on NetJets planes, and in 2015 told Berkshire shareholders "we have no anti-union agenda whatsoever."

The case is NetJets Association of Shared Aircraft Pilots v NetJets Aviation Inc et al, U.S. District Court, Southern District of Ohio, No. 23-01404.

(Reporting by Jonathan Stempel in New York; editing by Jonathan Oatis)