Migrant mothers and their babies are being put at risk because they are too frightened of incurring large debts and falling victim to the so-called hostile environment immigration policy to access vital medical care, a report has found.

Mothers who are not settled in the UK are not eligible for taxpayer-funded treatment, and are charged 50% more than the normal tariffs for antenatal care, births and postnatal care. Some with secure immigration status have also been mistakenly charged for treatment. Attempts at debt collection launched shortly after new mothers leave hospital can trigger mental health issues among some of the poorest and most vulnerable women in the UK, the research found.

Charging for NHS secondary care was introduced by Theresa May when she was home secretary as part of her “hostile environment” for immigration. The additional 50% on top of the cost of the treatment was part of a package of measures introduced in 2015 to incentivise the NHS in England to work harder to charge more effectively and consistently, as part of a crackdown on “health tourism”.

The report, What Price Safe Motherhood?, was launched on Tuesday by Maternity Action. The charity’s open letter to Matt Hancock, the health secretary, calling for the government to immediately suspend charging for NHS maternity care has been signed by more than 700 people, including heads of trade unions, NHS professionals and campaigners.

“Evidence from a growing number of studies and reports from migrant advice organisations shows that women at risk of [being charged] for maternity care are more likely to delay or avoid care because of fears of incurring large debts and of jeopardising the success of future immigration applications to the Home Office,” said Rosalind Bragg, the director of Maternity Action.

“Many of these women are poor or destitute, and are likely to have underlying health conditions which require regular antenatal care to provide the best chance of maintaining their own health and achieving good pregnancy outcomes.”

Provision of maternity care cannot be refused or delayed. But the report reveals women are frequently refused care if they cannot pay upfront for their treatment.

The normal NHS tariff for the cost to the taxpayer of antenatal care is £1,590 to £4,233. A straightforward birth with the shortest possible stay in hospital will cost around £3,282. Postnatal care can cost up to £1,207.50. Those deemed ineligible for NHS maternity care, however, pay themselves and are subject to a 50% surcharge on the usual cost.

The report collated interviews with 16 women of varying immigration status who were deemed ineligible for free maternity care, some erroneously. These included one woman with EU citizenship, a dependant of an EU citizen, a European Economic Area (EEA) national, and a woman married to a British citizen. It also includes women who were undocumented or refused asylum.

“All the women experienced additional anxiety and distress throughout different stages of pregnancy, with the undocumented specifically fearing detention or deportation if they were unable to pay,” said Bragg. “This fear discouraged them from seeking further maternity care during or after their pregnancy compounding existing health issues due to abuse or violence, and other medical and mental health issues. Those with secure immigration status still felt aggressed and also expressed diminished trust in the NHS and unwillingness to seek medical care in future.”

There are no reliable numbers of women affected by NHS charges for maternity services: women with insecure immigration status have difficulties coming forward if they are being pursued for debts. Wales and Scotland have different NHS rules. In addition, data is not centralised, with individual hospital trusts keeping their own numbers.

Beatrice, 30, came to the UK from west Africa as a student but was disowned by her family and her boyfriend when she became pregnant.

Her new partner became violent but she was unable to report him to the police because she feared being deported. She was eventually able to leave him three weeks before her due date with the help of church members.

Beatrice was given a bill for more than £3,000 the day after her baby was born and began to be harassed by a debt-recovery company. The Home Office sent a letter to her baby saying that he was “a dependent of someone liable to be detained”.

“It’s just me alone with my new baby and the debt people are calling me all the time, telling me: ‘You have to pay.’ I almost went mad,” she said. “It’s my first child. I’ve got no experience. The Home Office is on my back. I just can’t deal with it.

“I’m still trying to get over the nightmare that this is happening and I have to deal with it all alone,” she added. “There was a point I felt like just dying.”

The Department of Health has been approached for comment.