Brockton-based HarborOne Credit Union must be pretty confident that its board of directors and members will approve its proposed conversion to a mutual cooperative bank.

Last week, the $1.8 billion credit union “disaffiliated” from the Massachusetts Credit Union League and the Credit Union National Association (CUNA).

According to Rob Kimmett, a league spokesman, HarborOne provided the league with no rationale for its departure.

But in an email to Banker & Tradesman, HarborOne President and CEO James Blake said the institution’s proposed conversion may have become a distraction.

Blake has been a league board member for about 15 years.

“I have great respect for [league President and CEO] Dan Egan,” Blake wrote. “I just felt that given the direction we were heading in might create conflict on the board, which I didn’t want to do. I just felt the appropriate thing to do was resign…They have done great work for us in the past but under the circumstances our direction is changing.”

“We are disappointed when any credit union decides to no longer be part of the national trade group for credit unions,” CUNA Spokesman Patrick Keefe told Banker & Tradesman.

He said CUNA “believes there is strength in numbers and in unity,” but was careful to point out that if HarborOne’s board and members vote in favor of conversion after careful consideration, then the trade group has little latitude for argument.

HarborOne’s board of directors is scheduled to vote on the proposed conversion March 21. If it votes against the changeover, the effort dies. If it approves it, HarborOne will begin a three-month process of informing members about the particulars of the conversion and gathering their votes by secret ballot.