Two out of five low-paid young parents who ask for flexible work arrangements are "penalised" with fewer hours, worse shifts and even losing their job, a new report says.
A survey of 1,000 young mums and dads by the TUC found that more than half of those working in low-paid sectors such as retail, hospitality and social care, did not know their employment rights, with many unaware of unpaid parental leave arrangements.
Many of those polled had to take sick leave or holiday to cover childcare, while some said they were prevented from leaving work in an emergency.
Issues such as flexible working and work-life balance did not apply to many of those questioned, said the TUC.
General secretary Frances O'Grady said: "Too many workplaces expect mums and dads to forget all about their kids as soon as they walk through the door, but it's a nightmare to plan childcare when your boss changes your shifts at the drop of a hat, and you never work the same weekly hours twice.
"Many parents fear losing shifts, taking unpaid leave or being viewed badly at work if they need time off to look after their kids, and it is shocking that some mums and dads are being stopped from taking their children to hospital when they are sick.
"All workers should be given notice of their shifts at least one month in advance. Everyone at work should get the same parents' rights from day one, and everyone should be given written information about these rights."
The TUC criticised the attitude of some employers, saying more than two out five men surveyed felt "stigmatised" at work because of needing flexibility for childcare.
The report said many young parents are penalised if they ask their employer for flexible working arrangements, telling the TUC they are subsequently given fewer hours, worse shifts or even lose their job.
Ben Wilson, Equality and Human Rights Commission executive director, said: "We must radically overhaul our culture and make flexible working the norm.
"We have been calling for all jobs to be advertised as available for flexible working in order to remove the barriers people, particularly parents, face to increased pay and fulfilling careers.
"We also believe fathers should be given extra 'use it or lose it' paternity leave to encourage more men to ask for flexible working, reducing the 'motherhood penalty' that many women face."
A Business Department spokesman said: "The continued strength of our economy is built on the flexibility of our labour market, benefiting both business and workers and leading to record levels of employment.
"But that flexibility needs to work both ways which is why we commissioned Matthew Taylor to review modern working practices to ensure our employment rules and rights keep up to date to reflect new ways of working. We are considering his report carefully and will respond in due course."
Sarah Jackson, chief executive of the Working Families charity, said: "Younger parents are more likely to share care than the generations before them, and value flexibility at work highly.
"But the UK labour market is short-changing them. All too often a low-paid, insecure job, where the flexibility is all one way, is their only option if they want to work and care for their child."