Activists said they released thousands of insects into the burger chain’s Central St Giles and Holborn branches on Friday evening.
They accused Byron of carrying out “underhand entrapment” of its workers after 35 people were removed by immigration officials earlier in July.
London Black Revs & Malcolm X Movement said in a joint Facebook statement on Saturday they had taken “affirmative action” in response to the chain’s “despicable actions in the past weeks having entrapped waiters, back of house staff and chefs in collaboration with UK Border Agency”.
“Many thousands of live cockroaches, locusts and crickets into these restaurants.
“We apologise to customers and staff for any irritation, however, we had to act as forced deportations such as this and others are unacceptable, we must defend these people and their families from such dehumanised treatment,” it continued.
Earlier this week the Home Office said 35 people from Albania, Brazil, Nepal and Egypt were arrested for immigration offences at a number of restaurants across London, following an operation carried out with the “full co-operation” of Byron in July.
The burger business carried out the correct “right to work” checks on staff members, but had been shown false or counterfeit documentation, and will therefore not face civil penalty action, the Home Office said.
A Byron spokeswoman said: “The safety of our customers and restaurant teams is paramount, and our priority is now to work with local police to minimise the risk of further incident.”
The two London branches closed on Friday night and opened later than usual on Saturday after pest control visited.
On Twitter, the hashtag #BoycottByron is being used to encourage people to take their custom elsewhere.