BOSTON — Hundreds of unionized Massachusetts janitors voted to authorize a committee negotiating a new contract with their employers to call a strike.

The vote on Saturday comes as their contract is set to expire at month’s end. Janitors complain that employers offer them as few as 18 hours a week, a move that prevents them from qualifying as full-time workers and deny them access to insurance provided by employers.

About 1,400 janitors represented by Local 615 of the Service Employees International Union voted Saturday by a standing vote to authorize a strike. The union cited reports of workers being met with illegal threats and intimidation.

The Local 615 of the SEIU represents 18,000 property service workers — including 14,000 janitors — in Massachusetts, New Hampshire and Rhode Island. The union says more full-time jobs creates stronger economies.

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