A US mother-of-two has spoken of her frustration that she was forced to dump 500oz (14.8 litres) of breast milk at security at London's Heathrow Airport.
In an open letter posted on Facebook, Jessica Coakley Martinez, who was travelling without her eight-month-old son, said she felt "humiliated".
"You made me dump out nearly two weeks worth of food for my son," she said.
Heathrow says the UK government's rules on carrying liquids on planes are set out for passengers on its website.
The rules, set out by the Department for Transport, say that liquids may only be carried in containers holding 100ml or less in a transparent and re-sealable single bag.
The website says exceptions are made in the case of baby food or baby milk but only if the passenger is travelling with a baby. It says excess liquids should be carried as hold luggage.
Ms Martinez wrote that, although she should have looked up the rules, the regulation that breast milk was not allowed if the mother was travelling without her baby was "incredibly unfair and exclusionary in consideration of all of the other working mothers like me".
She wrote: "If I acted irate, it's because it was the only appropriate reaction I could muster.
"I now don't have the option to solely breastfeed my son because I don't have enough milk to supply him while I'm at work, despite all of my best efforts.
"Being a working mother and ensuring both my job and my child get exactly what they need is the hardest thing I've ever done but you managed to make it nearly impossible in a single afternoon.
"Security is the priority, but it isn't and shouldn't be your only goal, and it certainly shouldn't punish those you intend to protect.
"Beyond literally taking food from my child's mouth, you humiliated me and made me feel completely defeated as a professional and a mother."
She said that of the breast milk she was carrying "more than 300oz of that milk was frozen. Solid."
She continued: "I was willing to let go of the liquid milk. But you also wanted the solid milk because it could 'melt and become a liquid'."
Rules restricting the amount of liquids which can be carried as hand luggage on flights leaving UK airports were brought in in the wake of the discovery of a terrorist plot to detonate liquid explosives on board seven transatlantic airliners in 2006.
La Leche League, a charity that provides support to breastfeeding mothers, agreed that having to "unexpectedly discard milk expressed for a child is often very distressing".
"When a mother is away from her child she needs to express milk for her own comfort and to maintain a supply for her child. Not expressing her milk may lead to mastitis or engorged breasts and a drop in milk production. Having expressed this milk to take home for her baby, it can be very upsetting to be told to throw it away," spokeswoman Anna Burbidge said.
The charity said it recommends mothers travelling with expressed breast milk check the guidelines with the airline they are using before they travel.
Breast milk can be put into check-in luggage and knowing that beforehand may help a mother to plan how to transport the expressed milk, La Leche League added.