New mothers are facing increasing discrimination when they take maternity leave including being made redundant and switched to zero-hours contracts.

Citizens Advice has recorded a nearly 60% rise in the number of women seeking advice about maternity leave issues this year. Just over 3,300 came to the charity with such issues in the year to June compared to 2,099 last year.

The surge in reported problems has emerged after the Guardian revealed that Sports Direct workers returning from maternity leave are claiming they were moved on to zero-hours contracts. The claims were made in court documents relating to a breach-of-contract case in which workers say they were excluded from the retailer’s generous bonus scheme.

Citizens Advice says the introduction of fees for employment tribunals, through which workers can challenge poor treatment, has combined with the rise of zero-hours contracts, agency work and multiple part-time jobs to make employees more vulnerable to sharp practice on maternity rights.

Legally, women are protected from losing their job, having their hours changed or their responsibility reduced as a result of pregnancy. While employment and sex discrimination legislation offers protection, responsibility for enforcing such employment rights is spread across a wide range of agencies, from HMRC to the Gangmasters and Labour Abuse Authority, said Gillian Guy, chief executive of Citizens Advice.

“This confusing landscape means some bad bosses are getting away with treating their employees unfairly,” Guy said. “There is an opportunity for the government to consider bringing together the expertise of all current labour market enforcement functions into one well-resourced, effective body to investigate bad practice.”

Citizens Advice said the most common issue it dealt with in relation to maternity leave was being made redundant followed by a reduction in hours, including being moved to a zero-hours contract and having a role changed upon return to work.

A report into the issue, released by Citizens Advice this week, highlights the case of Nadia, who worked as a head chef in a local pub on a permanent contract. When she had difficulties during her pregnancy that meant she could no longer work in the kitchen she was offered work as a waitress on a zero-hours contract.

Another woman, who works for a national retail chain, told the Guardian she had her hours cut from about 34 a week to 26 during her pregnancy after she arrived late for work on one occasion.

“They said it was for my safety but that didn’t make sense. I was fine,” she said. Although she worked regular hours on the shop floor, she was employed on a zero-hours contract basis and found it hard to ensure she received any maternity pay.

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Now back at work, she feels under pressure to work even when her child is ill or she has given several weeks’ notice that she needs time off because of difficulties in finding childcare.

“I don’t really feel secure. Sometimes it feels like I have to go in or they will reduce my hours to nothing or I will lose my job. It’s always at the back of my mind when my daughter is not very well.”

The research by Citizens Advice supports the findings of a report by the Equality and Human Rights Commission into maternity discrimination published last year.

The study estimated that around 54,000 new mothers are losing their jobs across Britain every year – almost twice the number identified in similar research undertaken in 2005.

It also found that 10% of women were discouraged from attending antenatal appointments by their employers, putting the health of mother and baby at risk.