The Hawaii Regional Council of Carpenters is expected to announce today that the union will endorse U.S. Sen. Brian Schatz over U.S. Rep. Colleen Hanabusa in the Democratic primary for U.S. Senate.

The 6,300-member union is among the most politically influential private-sector labor organizations in the state.

"Sen. Brian Schatz has proven that he can deliver for Hawaii in the U.S. Senate and made sure Hawaii continues to receive our fair share of federal dollars in the appropriations process," Ron Taketa, the union’s executive secretary-treasurer, said in a statement.

Schatz, who was appointed by Gov. Neil Abercrombie in December 2012 to replace the late U.S. Sen. Daniel Inouye, has drawn several important labor endorsements.

The union backing helps Schatz answer Hanabusa’s contention that she is the more qualified and experienced candidate to deliver for Hawaii in the Senate. Many political analysts also presumed that Hanabusa, a former labor attorney, would score much better with labor than Schatz.

The two Democrats have essentially split the major public-sector unions. Schatz has won the support of the Hawaii Government Employees Association, the University of Hawaii Professional Assembly, and the State of Hawaii Organization of Police Officers. Hanabusa has earned the backing of the Hawaii State Teachers Association and the United Public Workers.

The candidates also have divided some of the most politically active private-sector unions. Schatz has the Carpenters Union and the Iron Workers’ Local 625, for example. Hanabusa has the International Longshore and Warehouse Union Local 142.

The teachers union support for Hanabusa, made quietly around the holidays in December, could be tactically critical for the congresswoman. The 13,500-member union is known for deploying teachers at the grass-roots campaign level.

Wil Okabe, the president of the teachers union, is in Washington, D.C., meeting with the National Education Association. Sources have said the NEA, the parent of the Hawaii teachers union, has not signed off on an endorsement. Okabe said he planned to ask the NEA today to back Hanabusa.

Schatz, meanwhile, said union carpenters "are the very definition of the good middle-class jobs we need to support. The carpenters represent a dedication to hard work, family and community — the Hawaii values I’m fighting for every day in the U.S. Senate," the senator said in a statement.

"The outpouring of support we’ve received has been humbling … "