Members of Harbor­One Credit Union in Brockton have approved the institution’s plan to become a state-chartered cooperative bank later this year, the credit union said Monday.

Senior vice president James Rice said the conversion, which must be reviewed by regulators, will probably take several months to complete. After the conversion, HarborOne, now the second-largest credit union in Massachusetts, would be a cooperative bank mutually owned for the benefit of its members and the community, rather than a stockholder-owned bank.

About 62 percent of the 22,000 members who voted backed the conversion. The bank has about 140,000 members.

HarborOne said the conversion will allow it to open branches and serve customers in Boston and other areas outside its traditional membership territory. It will also be free of credit union limits on commercial lending.

HarborOne, which has $1.8 billion in assets, is second in size to Digital Federal Credit Union.