The restaurant is refusing to serve those who look under 18, unless they can provide ID, after reports of large groups of youths causing a nuisance during the holidays.
The ban was introduced after a spate of anti-social incidents at the Buckshaw Avenue branch, with reports of teenagers spitting on the floor, throwing food and harassing staff.
Police have been repeatedly called to the restaurant this week to deal with the troublemakers, who have refused to leave when asked by staff.
"It’s not just a few bad ones,” said one staff member. “There’s at least 15 that come in every single day and harass all the staff by chucking food, sauces and spitting all over the floors.
"It’s because there’s so many of them, we can’t tell who causes chaos and who doesn’t, so we just have to refuse service to all teenagers.
"Hopefully they will stop showing up and we can start serving young people again.”
On Tuesday (April 5), KFC told the Post some staff members had been threatened with violence and said it was “working with local police to find a solution”.
A KFC Spokesperson said: “The safety of our team members remains our top priority. They, like anyone else, deserve the right to work in an environment that is free from threat and abuse – and some of the behaviour that our team members are seeing at Buckshaw Village simply won’t be tolerated.
"We are not banning all under 18s from our restaurant, but we are taking steps to make sure it is safe for all.”
But the ban on teenagers has not proved popular with some parents, including those whose children have been barred.
One Buckshaw mum who sent her teenage son to pick up an order was outraged after he returned empty handed.
“Absolutely pathetic that KFC won't serve teenagers now,” she said.
"My son just went to buy our food and was refused. Just because of a few bad ones.
“My lad works hard and hardly goes out of the house. He isn't one of the youths that have been hanging round there, so I don't see why they are punishing them all.”