A boom in the popularity of Pampas grass with interior decorators has led to "droves" of people picking the plant which grows wild near a beach.
The grass, near Littlehaven Beach in South Shields, forms part of a wind defence to stop sand blowing onto roads and helps protect the coastline.
South Tyneside Council warned anyone found removing it could be prosecuted.
Councillor Ernest Gibson said while the grass may look "beautiful in vases" people were "damaging the environment".
The grass, which was popular in the 1970s, can sell for up to £40 a bunch and has proved a popular addition to people's homes.
It is thought that photographs on social media sites such as Instagram may have influenced people turning up and taking it, Mr Gibson added.
'Benidorm without the sun'
"Pampas grass is quite expensive to buy if you went to a florist. It's cheaper to come to South Tyneside and take it away," he said.
"But what we are doing is urging people not to come here and take it away, it's there for a reason."
The Pampas grass helps to bond poor soils found at the coast, while Marram grass helps to prevent erosion in the dunes.
Signs are to be erected warning people not to pick the grass because it is already in need of replenishment, the council said.
"Through Covid, we have a massive amount of people coming to the coastal town, it's Benidorm without the sunshine," he added.
"It's great to see people at the seaside enjoying it [the grass] and that's what it's part of. It's there for everybody to view."
Garden designer George Wright said Pampas grass was "very popular" and he had seen demand increase two or three times at his nursery in West Boldon. He also expressed concern for the area.
"Once they take the flower heads themselves they take the seeds. Eventually this will become very much a patchy area and they will all start to decline.
"Pampas grass is becoming more and and more popular at the moment and I think a lot of it is people are starting to extend their houses into the garden so they want something nice in there, and also it's being used for interior decoration in houses."