Janitors in Greater Boston came to a tentative agreement with employers to avoid a strike Friday.

Hours before the previous contract was set to expire, the union representing 13,000 janitors in the area agreed to the new deal with Maintenance Contractors of New England.

Under the deal, which still needs to be ratified, maintenance workers will get annual wage increases of 12 percent, with Metro Boston janitors expected to make $20 an hour by its expiration.

The agreement was announced by 32BJ, a part of the Service Employees International Union.