WASHINGTON — Alan Gross, a former contractor for the United States Agency for International Development who has been imprisoned in Cuba for four years, plans to announce today that he has begun a hunger strike to help him win his freedom, a spokesman for Mr. Gross said.

Mr. Gross, who was arrested by Cuban authorities in 2009 and accused of being an American spy, has denied working for any intelligence agency. He is calling on Cuba to release him and is demanding that President Obama get involved in his case.

“I am fasting to object to mistruths, deceptions, and inaction by both governments, not only regarding their shared responsibility for my arbitrary detention, but also because of the lack of any reasonable or valid effort to resolve this shameful ordeal,” Mr. Gross said in a statement released on Tuesday morning.

Scott Gilbert, Mr. Gross’s attorney, also criticized U.S.A.I.D. for recent reports that revealed that the agency tried to secretly create a Twitter-like communication system called ZunZuneo in Cuba even as Mr. Gross was incarcerated. Mr. Gilbert said the agency should have known that the effort could threaten Mr. Gross’s safety.