Nazanin Zaghari-Ratcliffe, the British-Iranian woman jailed in Tehran, is being given less access to her family, her husband says.
Richard Ratcliffe said new rules mean she cannot make international calls to him in London – and can only see their five-year-old daughter once a month.
The UK government says it “remains extremely concerned” about her welfare.
Mrs Zaghari-Ratcliffe, 40, was jailed for five years in 2016 after being convicted of spying, which she denies.
She was detained at Tehran’s Imam Khomeini Airport after visiting the country to introduce her daughter, Gabriella, to relatives.
Mr Ratcliffe, from West Hampstead, said his wife was returned to prison on Saturday after being discharged from hospital, following a hunger strike.
Gabriella is living with her grandparents in Iran and the campaign group Free Nazanin said Mrs Zaghari-Ratcliffe told her family the restrictions were cruel and unjust.
According to the Guardian, she had previously been able to visit her mother in prison “every few days”.
“I am so upset,” Zaghari-Ratcliffe is reported to have said. “I feel like I could suffocate. I can’t even think what to do. I haven’t cried so loud… for ages.”
Mr Ratcliffe told the BBC his wife has written to the Iranian prison authorities to protest against the changes.
“The phone calls is one thing but not being able to see Gabriella… that’s really tough”, he said.
He added: “Boris Johnson, when he was foreign secretary, made a clear promise to leave no stone unturned we want to hold him to that promise.”
In response, the Foreign Office said it was “deeply concerned” over the restrictions on Mrs Zaghari-Ratcliffe’s access to her family. It said Foreign Secretary Dominic Raab plans to raise this case with Iran’s foreign minister and to meet Richard Ratcliffe soon.
A spokesman added: “We continue to regularly raise her case at senior levels, including our embassy in Tehran pressing for consular access and we are in regular contact with Mrs Zaghari-Ratcliffe’s family.”
Ten-year jail sentence for UK resident
Campaigners say Mrs Zaghari-Ratcliffe was temporarily denied contact with her husband in January after announcing her first hunger strike.
In March, then Foreign Secretary Jeremy Hunt granted her diplomatic protection – theoretically opening up the possibility of Britain taking international legal action against Iran.
Meanwhile, there are reports a UK resident has lost her final appeal against a 10-year jail sentence for spying for Britain in Iran.
The Times says Aras Amiri, an Iranian citizen with permanent residency in the UK, refused to make a false confession in return for her freedom.
In a letter to the head of the Iranian judiciary, Ms Amiri, 34, said she had been imprisoned solely because she had worked for the British Council.
Another British-Iranian dual national was also arrested in Iran last week, according to his family.
The wife of Kameel Ahmady, a social anthropologist, said he was taken into custody on Sunday without a reason being given.
Earlier this year, the UK foreign office warned all dual nationals against travelling to Iran because of the risk of arbitrary detention.
Diplomatic tensions between the two countries have been strained in recent months.
It follows UK forces’ involvement in helping Gibraltar seize a tanker which carrying Iranian oil, over fears it was travelling to Syria in breach of EU sanctions. The tanker – formerly known as Grace 1 but renamed Adrian Darya 1 – was released last week.
But Iran still holds the British-flagged Stena Impero tanker which it seized in the Strait of Hormuz on 19 July.
Iranian Foreign Ministry has said a decision on whether to release the ship depends on the Iranian Judiciary.