Wholesale produce distributors say demand is exceeding supply of iceberg and romaine lettuce, and pricing pressures are expected to continue throughout the month.

Restaurants Canada COO Kelly Higginson said a major lettuce-growing area in California was hit by some kind of virus, after a year that's already been rife with difficulties thanks to heat and drought.

"That particular area has had crops decimated. So there's a massive shortage," said Higginson.

From fast-food joints to fine dining establishments, "everybody's just pulling lettuce off the menu," she said.

That's because not only is lettuce in short supply, but the available product has in some cases quadrupled in price, she said.

"There's no room for these restaurants to absorb more costs ... and somebody is only going to pay so much for a salad. So once the price gets to a certain point, they're just gonna have to take it off the menu," said Higginson.

Fast-food chain Subway said lettuce is temporarily unavailable at some of its restaurants, and anticipates supply will improve in late November.

In a tweet last week, Swiss Chalet's Canadian division said due to the industry-wide shortage, its garden and Caesar salads are not available, and items that normally contain lettuce, like burgers, will come without lettuce for the time being.

Higginson said events like this have become more common in the past few years, leading some restaurateurs to offer smaller menus or use seasonal produce to try and avoid the impacts of supply inconsistencies.

She said if a large number of restaurateurs pivot to other greens like spinach or kale, prices of those products could also rise.