Supermarket giant Tesco has rationed customers to three iceberg lettuces per visit – blaming poor growing conditions in Europe for a shortage in UK stores.
It said bad weather in Spain had caused “availability issues” but suppliers were working to resolve the problem.
Morrisons has also limited shoppers to three heads of broccoli and three iceberg lettuces, the Daily Mail said.
It follows a UK courgette shortage last month, after wet and cold weather in southern Europe devastated crops.
Customers have posted photographs on social media sites of empty lettuce shelves in Tesco stores, alongside signs asking them to limit lettuce purchases.
One notice read: “Due to continued weather problems in Spain there is a shortage of iceberg lettuce.
“To protect the availability to all our customers, we are limiting bulk purchases to three per person. We apologise for any inconvenience caused.”
A Tesco spokesperson said it had introduced the limit to ensure its stores did not run out of some products.
A Morrisons spokesman told the Daily Mail it had introduced a cap to stop local businesses and restaurateurs buying up all of its stock.
“As a result of the fact that the Spanish harvest has been very difficult this year, we have just about enough coming in to supply our customers,” he said.
Meanwhile, Sainsbury’s told the paper it was working with suppliers “to maintain supply for our customers”.
Dieter Lloyd, from the British Leafy Salads Association, told the BBC that flooding in Spain before Christmas had damaged crops, and grounds were then too wet to grow a fresh batch.
The problem was compounded by a cold snap of weather in January, stopping farmers going out and planting.
“Southern Spain provides around 80% of the fresh produce for the EU out of season, so it is not just the UK,” he told BBC Radio 5Live.
“There are still stocks coming in, albeit at a reduced rate – I have seen it is as low as 30-50% of what we normally have – but the challenge is we are not the only people buying it.
“With Germany, France and the rest of the EU too, the people who are prepared to pay are going to get it.”
And Mr Lloyd said there was not a clear end in sight to the shortage.
“This won’t solve itself this month or next,” he added.
“For this season, their crop has been devastated.”
Iceberg lettuces currently being stocked in UK supermarkets have probably been grown in California, rather than Europe.
Last month, fruit and vegetable wholesaler Nick Padley told BBC News that getting the crop elsewhere came at a cost.
He said: “There’s a gap of about six weeks on iceberg lettuce, nothing is coming from Spain for six to eight weeks.
“Our supplier is now going to be bringing in iceberg from America which is obviously costing more. It’s a tough time.”
The supply of other vegetables – including aubergines, tomatoes, broccoli and peppers – grown in Europe is also down.
The Spanish association of fruit and vegetable producers, FEPEX, said it expected the shortage of leafy vegetables grown outdoors, including lettuce and spinach, to continue until early April.