Nazanin Zaghari-Ratcliffe, 40, a project manager with the Thomson Reuters Foundation, was arrested in April 2016 at a Tehran airport as she headed back to Britain with her daughter after a family visit.
She was sentenced to five years in jail after being convicted of plotting to overthrow Iran's clerical establishment, a charge denied by her family and the Foundation, a charity organisation that operates independently of Thomson Reuters and Reuters News.
"Nazanin called me this morning to confirm from Evin prison that she has started this hunger strike this morning. It is initially a three-day hunger strike," her husband, Richard Ratcliffe, said.
He said Nazanin was taking the action to press demands for access to specialist doctors to address health concerns and to be allowed such treatment as they prescribed.
A spokesman for Iran's judiciary declined to comment.
Britain has said it will not let Zaghari-Ratcliffe's case rest and the BBC reported that Foreign Secretary Jeremy Hunt had summoned Iran's ambassador on Monday to discuss it. Britain's foreign office declined to comment.
Iran has said that the trial and the verdict are in the hands of the judiciary.
Monique Villa, CEO of the Thomson Reuters Foundation, said it was "extremely shocking to see our colleague ... going on hunger strike to protest at her inhumane treatment."
Britain has advised British-Iranian dual nationals against all but essential travel to Iran, tightening its existing travel advice and warning it has only limited powers to support them if detained. (Reporting by Alistair Smout Editing by Nick Tattersall)
(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)