More than 110 refugee charities are calling for a “kind and effective system” for those seeking asylum in the UK and have signed the letter to the Cabinet minister.
She has also said the only way for refugees to get into the UK is through a “safe and legal route”.
“Home Secretary, when you talk of ‘safe and legal routes’, you must be aware that it is impossible to ask refugees to come exclusively through such a path when even Afghan interpreters who are eligible for one of our few existing schemes remain in hiding from the Taliban,” the letter read.
“When you talk of ‘illegal migrants’, you must be aware that the top nationalities of people making dangerous journeys include Afghanistan, Eritrea and Syria, and that at least 97 per cent of asylum claims made by people from these countries are successful.
Migrant crossings on the English Channel surge amid heatwave — in pictures
“When you question the existence of ‘modern slavery’, you must be aware that you are dismantling your own party’s proud and internationally-recognised achievement in protecting the survivors of trafficking.
“And when you complain about the cost of housing asylum seekers, you must be aware that, while people seeking safety did not choose to leave their homelands, they are willing to work and keen to contribute, if only the law permitted them.
“You have referred to this country’s proud history of offering sanctuary, so we ask you to make this happen with a fair, kind and effective system for refugees.
Migrant children rescued in French waters — in pictures
“Deal with the backlog in asylum cases, create safe routes, respect international law, and the UN convention on refugees, and give refugees a fair hearing, however they get here. Then you would have really done something worth dreaming about.”
The letter, co-ordinated by charity IMIX and coalition campaign Together With Refugees, was signed by groups such as Choose Love, Christian Aid, City of Sanctuary UK, Doctors of the World, English National Opera, Freedom from Torture, Good Chance Theatre, JCORE, Jesuit Refugee Service, Rainbow Migration, Refugee Action, Refugee Council, Scottish Refugee Council, Safe Passage and Save the Children.
Afghan migrant documents dangerous journey across Channel — video
It came as almost 1,000 migrants arrived in the UK after crossing the Channel on Saturday.
Earlier this month, Ms Braverman said migrants crossing the Channel will face a ban from claiming asylum in Britain.
UK's first Rwanda deportation flight cancelled — video
“Every day in our therapy rooms torture survivors tell us about the hardship that 12 years of anti-refugee policies have caused them. Suella Braverman’s policy proposals promise to intensify their cruelty,” said Sonya Sceats, chief executive of Freedom from Torture.
“Braverman’s dream of flying refugees to Rwanda by Christmas seems even further from realisation after the airline hired to carry out the fights bowed to pressure from Freedom from Torture and pulled out of the scheme.
“This letter shows the depth of feeling against the government’s anti-refugee policies and that there are positive alternatives possible.”
The Home Office has been approached for comment.