The pay freeze and savage cutbacks announced by the coalition government will primarily affect women, who make up 85% of part-time workers in the civil service

Some of the fear being felt by women who work in the public sector can be seen in Newcastle. It is there that Natasha Nicholson, an outreach worker for Sure Start, jokes that next year she will be able to afford only beans on toast for her young family. "The reality is we might not even be able to pay for the bread," says Nicholson, 25, through a choked laugh.

And in Yorkshire, in Hebden Bridge, Lisa Ansell, a former civil servant and social worker, remembers settling down with a calculator after watching the chancellor, George Osborne, deliver his emergency budget. "I suddenly realised just how much I rely on public services: on subsidised public transport... on Sure Start."

Travel 290 miles south to Worthing, West Sussex, and there is Dee Luxford, 40, with her husband and three children. She and her colleagues in low management and administration roles at HM Revenue & Customs (mainly women) fear for the service they are providing. "If we tighten the belt any more, we are going to suffocate," she says.

All feel nervous about one thing: repeated reports that suggest the government's axe is hovering over them. Some claim that women will shoulder three-quarters of the pain as the most severe austerity measures in a generation start to take their toll.

It is those fears that led the Fawcett Society to launch its unprecedented legal challenge. In what is believed to be the first case of its kind, the women's rights group is seeking a judicial review to declare Osborne's emergency budget unlawful. They will find out if they are successful later this month.

The society claims that the government missed one crucial – and legally binding step – in its preparations for cuts: that it failed to carry out an "equality impact assessment" to show how the plans will affect women. If proved, it may be an expensive mistake. Ministers could be forced to redo their sums and present a study to parliament after all. In the most extreme case, MPs could be made to vote on the budget again.

"We could not stand by any longer and watch it take place," says Anna Bird, head of policy and campaigns for the society, who described the cuts as the biggest in peacetime.

It is research by the House of Commons library, commissioned by shadow minister Yvette Cooper, that claims women will suffer 72% of the tax and benefit cuts. After all, four in 10 working women are in public sector jobs – which will be hit by a pay freeze and projected net losses of 600,000 posts. The fact that women make up 85.4% of part-time jobs in the civil service also makes them feel vulnerable.

It is women, too, who are most likely to be dependent on a long list of benefits targeted in the budget.

The study highlights the cutting back of the Sure Start maternity grant, which will affect 262,000 women and no men. Perhaps unsurprising. But what of the decision to freeze child benefit? That is said to affect a disproportionate number of women. As for housing benefit reform, 2.9 million women will be affected against 1.9 million men. Then there are the tax credit reforms, and the removal of income support for lone parents when their children reach the age of five, instead of seven. Nine out of 10 single parents are women.

Emily Kelly, a representative for the Public and Commercial Services Union (PCS), is one of them. "Personally?" she responds when asked how the cuts will affect her. "I am a single parent. I am on a low wage. My pension is not gold-plated, more like tin-plated – just under £5,000 a year. I have been in the civil service for 23 years, but my compensation [redundancy] package is rubbish. Certainly not the £60,000 you read about in the newspapers. The attacks on tax credits and child benefit will affect me. I am worried about losing my job in a market where there are no others. And I work in a department with lots of other women – just like me."

It is stories like Emily's and Dee's, Lisa's and Natasha's – and the women they work with – that spurred on the Fawcett Society, which fears that progress on gender equality is about to be pushed into reverse.

"Women already experience economic inequality," said Bird, who adds that Fawcett was inundated with messages of support after news of the challenge emerged in the Observer last week. "Nine out of 10 lone parents are women; 30,000 women lose their job each year because they fall pregnant; we know that women are paid lower amounts for the same work. These inequalities are likely to be exacerbated by these cuts."

Fears also surround the impact on the poor, the disabled, the young and ethnic minorities. And they were hardened last week with the revelation that Theresa May, the home secretary and minister in charge of equality, had written to her colleagues to warn there was a "real risk" that the budget plans would affect women, ethnic minorities, disabled people and the elderly disproportionately. If the government could not show that equality issues had been fully considered, then a legal challenge had a real chance of success, she said.

For its part, the Treasury stresses that a "distributional analysis" was carried out alongside the budget, showing the impact on the poorest. As for gender, some suggest the House of Commons research exaggerates the effect on women because it fails to consider the fact that benefits targeted at families help men as well. Departments will consider the impact on equality when drawing up plans for cuts to be announced in the comprehensive spending review in October. But lawyers claim that is too little, too late.

It is little reassurance for people such as Dee Luxford, speaking as a PCS branch representative. "Gone are the days when women worked for holiday money. Many are the breadwinners in the home," she says. "I know I am, and I earn £18,000. My husband is a builder and after he was hit by the recession works sporadically at best. Holidays are a thing of the past. We prioritise different bills each month – water, electric, gas – nothing is paid on time. We don't even want to spend money on prescriptions." Luxford says rents in the south of England are astronomical.

Emily Kelly is equally terrified. She works in north-west England in an office filled with women. She earns £17,500 and is a single parent. She worries about what will happen if she loses her job. "The market is going to be saturated by people looking for employment, and we in low management will be down the list. There are going to be professionals looking for work.

"And my children may as well stay in education because there is nothing out there. It is getting quite grim, and autumn is going to be awful."

One of her biggest beefs is the perception of the civil service being propagated by the government. She believes ministers want to divide the country in two and denigrate the public servants. "We are not these white, middle-class, bowler-hatted mandarins from Whitehall. There may be 10 of those in London but the average public sector worker is someone who works solidly on vital services: getting people into employment, processing tax credits, registering the land. If they take the bulk of that away..." she pauses and then quickly adds: "I think the economy will collapse."

She thinks even friends look down on public servants. "It is like, 'You deserve this because you have had it good for so long.' But that is absolute rubbish."

Emily's experience builds up the sense of a mood that is being seen as anti-women. She talks about "a bizarre move" by her employer to consider removing a sanitary towel machine to save costs. And it is reviewing childcare offerings, something that seems to be happening across the country in councils, universities, colleges and other public bodies. If nursery options are cut back it will be a double whammy for women.

Union leaders are furious. Mark Serwotka, general secretary of the PCS, says the budget is little more than "political savagery" but, he adds, perhaps unsurprising with such an unrepresentative cabinet. Ministers should be hanging their heads in shame, he says.

And Labour, of course, will not miss this opportunity. Cooper, the shadow work and pensions minister, describes the budget as the "biggest attack on women in generations". She adds: "No government can be above the law. Fawcett are right to challenge this all the way through the courts."

'They don't understand what it's like'

Natasha Nicholson, 25, is a Sure Start outreach worker in Newcastle upon Tyne. She is married to Paul, 29, and has a daughter, April, 4.

Natasha Nicholson knew long before the budget that she would become vulnerable under this government. Her job was named in the coalition agreement, published in May, as one that could be hit.

She works in a deeply deprived community in west Newcastle helping families to get the services provided by Sure Start and others. "It is hitting from every angle. A lot of staff at Sure Start are women, but so are a large proportion of those using the service as well. There are a lot of lone parents."

Her husband, Paul, works in the private sector as a print finisher and was hit hard by the recession when he was not paid for five months. Natasha remains unconvinced by the argument that as the public sector is cut back the private sector will rise in its place. Instead, she fears it, too, will be hit. "It is a vicious circle. I am on £20,000 and my husband on £15,000," she adds, saying she is terrified of losing her job.

"We have to pay for the house, the gas, food, general amenities," she says. The couple have just spent £100 on a school uniform for April. "That is money we don't have. I know going on holiday is a luxury," she adds, explaining that they will not have a break this year. "I feel the coalition government, particularly the Tories, don't have an understanding of what it is like to be a working-class person just getting by."

'It's ingrained in me that I should work'

Lisa Ansell, 32, is setting up a business in Hebden Bridge, Yorkshire. A single parent with one daughter, Rachel, 3.

Lisa Ansell says she realised straightaway that women would be particularly hit. She got calls from two friends that night with young children who felt the reforms would make returning to work harder. Ansell had worked in the civil service before moving into social work. She had been offered a job at a local school, liaising with social services, but after the budget it was withdrawn.

Next day she wrote on her blog, DeeplyFlawedButTrying. The piece was entitled "The Budget and Me!" and explained how she had worked 30 hours a week as a social worker and managed her child and house. "It is ingrained in me that I should work," she wrote. Ansell is unhappy about changes to housing benefit, saying it would make her worse off if she returned to work. The reality behind the "rhetoric of fairness", she added wasn't "very damn fair to me, or my daughter, or the thousands of women in the same position".

Now Ansell is setting up a business, Calder People, which helps people in the area to work remotely for companies. She is angry about the way she sees ministers denigrating public servants. She feels that those like her who spent years working to help people back into work are having their contributions reduced to "leeching". And it is those same people, she adds, who will bear the brunt of the cuts with caps to salaries and pensions and the fear of losing their jobs.