The broadcaster claims Iran has "stepped up a campaign of intimidation"
The BBC is making what it calls "an unprecedented appeal" to the United Nations to stop Iran from harassing its Persian service staff.
It says both its workers in London and their families in Iran have come under threat.
The broadcaster claims Iran has "stepped up a campaign of intimidation" - including threats, arrests of relatives and travel bans.
It says Iran began targeting its Persian service after a disputed presidential election in 2009, when Tehran accused foreign powers of interference.
The appeal is being made at a meeting of the UN Human Rights Council in Geneva.
The BBC says its Persian staff are unable to travel back to Iran for fear of arrest.
It says her 27-year-old sister was taken by security agents during a raid on her father's home in Tehran.
"When I said no, they kept my sister in solitary confinement for 17 days," she says.
While the corporation says the elderly mother of a senior producer was called in for questioning by an intelligence agency in Tehran.
"She was told that her son could have a car accident in London if he continued working for the BBC", the broadcaster says.
"She took the threat very seriously - as did the counter-terrorism police in London, who immediately made arrangements for his protection."
Jamie Angus is director of the BBC World Service Group: "We've asked the Iranians privately and publicly to desist for this harassment - and in fact it's got worse in the last 18 months or so.
"Your listeners should be aware of what's actually at stake here: for our Persian service staff who are based in London - we don't have staff based in Iran - they can't return to Iran under fear of arrest, their families are often prevented from leaving Iran by having their passports taken away, (and) the families are also intimidated by the security services.
"But most worryingly, there's been an entirely spurious national security case been launched recently, which has effectively frozen the assets of many of the families of up to 150 Persian service staff.
"We just feel this is completely unacceptable - we're not being treated in this way by any other country in the world".
"We're not treated in this way by any other country in the world"— BBC World Service (@bbcworldservice) March 12, 2018
Why the BBC wants #Iran to stop harassing its @BBCPersian journalists and their families: https://t.co/mrHpphJrEM (with @grvlx001) pic.twitter.com/SNALyXckXR