One in three breastfeeding mothers have been forced to use a toilet when they express milk after they return to work, according to a survey.
More than half said they have had to express in an unsuitable place, including the staff room, their car or their desk and highlighted a lack of workplace support after having a baby.
As a result, almost a third said they have experienced problems while trying to express, including issues with their supply, infections and anxiety.
These difficulties resulted in 30% of mums stopping earlier than they would have liked.
One 36-year-old pharmaceutical worker, who has remained anonymous because she feared losing her job, said her employer had not provide adequate facilities to express milk while at work.
The mother-of-one said: "At head office there isn't a specific room to use, so I have to try and find an empty office or conference room, which don't have locks or any privacy. I've had to use the toilets on many occasions.
"Sometimes I've just gone back to the car park and expressed in my car.
"It's not acceptable but I don't really have a choice."
Employment law states that breastfeeding staff should have a place to rest, but there is no requirement for workers to have paid breaks to express milk or feed their baby.
Half of breastfeeding mothers said their bosses did not know what to do, had no facilities or felt embarrassed by the conversation, according to the survey by the law firm Slater and Gordon.
One of the firm's employment law specialists, Paula Chan said: "This research is concerning- no mother should feel forced to express milk for her child in a toilet.
"People would be horrified at the thought of food being prepared in such unhygienic conditions so it's unacceptable that we are in a situation where that is considered to be an option when preparing milk for a baby."
The anonymous worker who provided a case study also said there was no storage facilities for her expressed milk, so it had to be thrown away - something she said was "heart-breaking".
The mother of one added: "There was a time when I first started with the company and I could feel myself lactating.
"I hadn't had the chance to express before the meeting had started and ended up leaking all over my shirt. I had to spend the rest of the meeting trying to cover the wet stains with my blazer.
"I didn't feel I was able to leave and just sat there. It was so embarrassing."
The research polled 2,000 breastfeeding mothers who had a baby within the last five years.