Janitors who work in Penobscot County-owned buildings decided this week to join a union.

Wednesday’s unanimous vote, which capped a process that started in May, makes the half dozen or so maintenance workers the fourth group of county employees to join the American Federation of State, County and Municipal Employees. It also ends a controversy of sorts that threatened to lead to a formal complaint over anti-union lobbying by a supervisor.

The custodians reportedly approached the union in May and the union collected enough signatures to pursue the matter. The county commissioners approved the janitors in June as an “appropriate bargaining unit,” and AFSCME petitioned the Maine Labor Relations Board to hold an election.

In June, the commissioners issued a warning to the department supervisor, Earle Hamel, who reportedly attempted to dissuade his workers from organizing. Had the workers decided against the union, AFSCME could have filed a formal grievance. The positive vote, however, pre-empted such action.

Sheriff’s Department supervisors, patrol and corrections officers, and the county’s clerical workers already belong to AFSCME. Eventually, the maintenance and clerical workers could form a single unit.