CAMBRIDGE, Massachusetts — An advocacy group for the deaf on Thursday sued Harvard University and the Massachusetts Institute of Technology, saying the prestigious schools had violated laws by posting online video and audio recordings for public use that lacked accurate captions.

Two lawsuits charged that Harvard and MIT said the webcast recordings were intended to provide the public free access to the schools but were unusable by people with difficulty hearing because they either lacked captions or had captions that were so poor as to be unusable.

“Harvard has largely denied access to this content to the approximately 48 million — nearly one out of five — Americans who are deaf or hard of hearing,” plaintiffs, including the National Association for the Deaf, said in a filing in U.S. District Court in Boston on Thursday.

The separate lawsuit filed against MIT contained similar language. Both suits seek class-action status.

The suits against the Cambridge, Massachusetts-based schools asked the court to find that the schools violated Title III of the Americans with Disabilities Act by failing to caption the programming and to order the schools to provide accurate captions in the future.

Harvard and MIT representatives did not immediately respond to requests for comment.