Boston’s First Trade Union Bank will soon become one of the few banks to offer its customers a mobile app for making purchases at brick-and-mortar retailers using their smartphones.

The community bank, which has two branches in Boston and two in New York, will launch the app early next year through a partnership with Scvngr Inc., a Boston start-up that operates the LevelUp mobile payments platform. The bank’s app will let customers use their iPhones or Android phones to pay at any of the 4,000 merchants nationwide that are on LevelUp’s network.