NationsHeritage, once known as the Texas Instruments FCU that has been serving a shrinking employee base, cited economies of scale as a factor in pursuing the merger.
The deal, slated to receive member approval at a meeting late last week, also needs the OK of State Banks Commissioner Steven Antonakes.
The merger will bring together "two credit unions with contiguous branch operations," and creates an enhanced product menu for NationsHeritage, said James Rice, senior vice president of marketing at the $1.7 billion HarborOne.
Maureen Tebo, president/CEO of NationsHeritage, which has two offices in Attleboro and one in Mansfield, said her CU has seen its membership decline with downsizing by Texas Instruments' Boston-area facilities.
In February, the CU sold its main office building to a real estate firm, agreeing to lease back part of it.
For years, dating back to the 1960s, the CU was known as TI FCU serving the firm's metals and controls employees. NationsHeritage has 7,000 members, while HarborOne has 138,000.