Boundless Learning Inc. says it will liberate college students from big textbook bills with free online versions built from public Web content.

But the Boston start-up is being accused of copyright infringement by three of the largest educational publishers in the world, who say it creates its texts by stealing from well-known textbooks. Boundless is “a business built on brazen infringement’’ that “misleads students, and has a corrosive effect on learning,’’ according to a lawsuit filed last month in US District Court in New York.