A former Sports Direct employee has launched a legal action against the company over its use of zero-hours contracts in a case that could set a precedent for hundreds of thousands of British workers hired under the controversial employment terms.

Zahera Gabriel-Abraham, 30, quit her job at the retailer after suffering panic attacks that she blames on her family's lack of financial security – the result, she says, of a contract that offered no guaranteed work or income.

Sports Direct prompted a furore over Britain's zero-hours culture when the Guardian revealed that 20,000 of its 23,000-strong workforce are employed under the contracts. McDonald's, Cineworld and Buckingham Palace subsequently emerged as zero-hours employers, leading to the Office of National Statistics revising up its estimates of Britain's zero-hours workforce by 25% to 250,000.

Gabriel-Abraham left the Croydon branch of Sports Direct, in south London, last month and is suing the retailer with the financial support of campaign group 38 Degrees. She said: "If you happen to fall out of line, or your manager thinks you have not done very well that week, your hours just get cut – you feel like you are just at the beck and call of the people above you.

"I felt I always had to play up to someone's ego just to work – and in the end you just start to feel a bit bullied.

"Regularly they would call you in the middle of the day and they are like: 'Can you come to work now?' You feel like you have to say yes because if you say no you are seen as unreliable and the next week you don't get a shift, it is as simple as that … I felt hugely manipulated and bullied the whole time."

David Babbs, executive director of 38 Degrees, said: "If the case is successful, we hope that this will set a precedent for zero-hours contracts."

Elizabeth George, a barrister at Leigh Day, who is acting for Gabriel-Abraham, said the contracts gave staff no job security while expecting them to fulfil the same duties as full-time colleagues.

She said: "We are not arguing that employers cannot have genuine flexible contracts, but the contract under which Ms Gabriel-Abraham worked, and which all SportsDirect.com 20,000 part-time employees appear to be working, has no flexibility at all for those people who sign them. There was no practical difference between the obligations put on my client by the company and those placed on full-time staff."

George added that zero-hours workers support the salaried staff by taking on their shifts at short notice when cover is needed or when shops experience a spike in consumer demand.

"In return for not having the security of knowing when you might work you have the benefit of being able to choose when you work. Without that choice you are not a casual worker, you are just a worker with no job security. The 'casual' part-time employees in this case are employees in the conventional sense and denying them their paid holidays, sick pay and bonuses is unlawful."

The group 38 Degrees has urged its members – 5,000 of whom have donated towards the legal costs of Gabriel-Abraham's case – to email Sports Direct executives to offer staff guaranteed hours contracts. More than 125,000 emails have been sent to chief executive Dave Forsey and head of retail, Karen Byers.

Babbs, of 38 Degrees, added: "Big businesses must be held to account and zero-hours contracts must not be used as a justification to abuse employees' rights."

The challenge comes in the same week that the company, owned by billionaire Mike Ashley, handed out shares worth nearly £140m to 2,000 full-time staff, with £112m cashed in on Tuesday. Part-time employees were not entitled to join the bonus scheme despite some working shifts of 40 hours a week for long periods of time.

Sports Direct declined to comment.