The UK government has defended its decision to resume the deportation of failed asylum-seekers to Zimbabwe.
Some 7,000 Zimbabwe asylum-seekers are thought to be in the UK
Some 500 Zimbabweans have been sent letters urging them to return voluntarily or face expulsion.
A campaigner told the BBC it was curious that the UK condemned human rights abuses in Zimbabwe and yet tried to force people to return there.
Campaigning for Zimbabwe's general elections later this month has so far been relatively peaceful.
But Sarah Harland from the Zimbabwe Association, which helps failed asylum-seekers, said that could change.
"Sending people back to Zimbabwe at this volatile time would be the wrong thing to do," she told the BBC's Network Africa programme.
"It is very curious that the government can be so damming about the situation in Zimbabwe and what a vicious regime but at the same time show such little compassion to those who have fled that regime."
Last year, a British judge ruled that not all Zimbabweans would face persecution if they were sent back home, overturning a ban on deportations after an earlier court ruling.
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The Border & Immigration Agency [BIA] has now written to some 500 failed asylum-seekers mostly in the north-west, saying:
"I am now writing to make sure that you know that the Border & Immigration Agency [BIA] is expecting shortly to be able to enforce returns to Zimbabwe... You have exhausted your rights of appeal and have no other basis of stay in the UK. You should now make plans to return home."
London's Independent newspaper says about 1,000 of some 7,000 Zimbabwe asylum-seekers in the UK are likely to be affected.
A UK government spokesman told the BBC that "not every Zimbabwean in the UK qualifies for asylum".
"We believe it is vital we continue to operate a fair and robust system, enforcing the removal of those not entitled to be in the country."
In his ruling last year, Justice Henry Hodge said only those linked to opposition parties were likely to face persecution.
But opposition activist Rudo Mawari told the BBC that she had received a letter threatening her with deportation.
She says she worked for the opposition Movement for Democratic Change and was attacked by thugs working for the ruling Zanu-PF party.
"I was sexually assaulted in front of my kids," she said.
"If I go back, I am still at risk. There is no way I am going to volunteer myself to return to the same situation I fled from."
The European Union and the US have accused President Robert Mugabe of rigging previous elections - charges he denies.
Zimbabwe has one of the worst performing economies in the world, with shortages of basic goods and just one in five adults believed to have a job.