WASHINGTON — A union is taking sides in Hawai'i's Democratic Senate primary, spending $100,000 on an ad backing incumbent Sen. Daniel Akaka.

The American Federation of State, County and Municipal Employees has bought air time for the 30-second spot that will run on broadcast and cable TV, starting at week's end. The money comes from the union's political action committee.

Akaka, 81, faces Rep. Ed Case, who is almost 30 years younger, in the state's Sept. 23 primary. Case has portrayed Akaka as aging and unproductive.

The ad says Akaka "is a strong ally of working families on issues like schools and Head Start, opposing Social Security privatization and protecting Medicare and Medicaid," said Paul Booth, executive assistant to AFSCME president Gerald McEntee.

"It's unusual but not unprecedented to support a candidate in a primary," Booth said. "Our support is based on the solidness of his record supporting working families."

Meanwhile, the National Association of Realtors, which has endorsed Case, has taken out ads in the Islands touting his support for small businesses.