Police in London are seeking three men in connection with two bizarre incidents in which cockroaches and locusts were released inside two restaurants.

The Metropolitan Police say an unknown number of male suspects walked into two different locations of the Byron burger chain on July 29 and “deliberately released” live insects onto the floor and inside men’s washrooms. Both restaurants were shut down for the day as a result.

Surveillance images of three men who police want to speak to in connection with the incidents were released on Tuesday.

The insect release occurred during protests against Byron, after some of its workers were rounded up in a U.K. Home Office immigration sting.

The Guardian newspaper has reported that Byron workers were allegedly told to attend a health and safety meeting in early July, but were met by immigration officials instead. At least 35 people from Albania, Brazil, Egypt and Nepal were swept up in the raid, according to The Guardian.

Activist groups London Black Revs and Malcom X Movement have claimed responsibility for the “biblical swarm of insects” released inside the burger joints.

“London Black Revs and the Malcolm X Movement have taken affirmative against the Byron restaurants chain in response to the despicable actions in the past weeks having entrapped waiters, back of house staff and chefs in collaboration with UK Border Agency,” the groups said in a statement posted on Facebook.

The statement says the insect release should “serve as a warning to other businesses in the hospitality and catering industry” that plan to “entrap migrant workers.”

“We apologise to customers and staff for any irritation, however, with the growing climate of racism and xenophobia, a line must be drawn and we say, enough is enough,” the statement said.

Many customers are also lashing out against the burger chain online, using the #boycottbyron hashtag.

In its own statement, the Byron chain said it was unaware that any of its workers “were in possession of counterfeit documentation” until the U.K. Home Office brought it to management’s attention.

“We carry out rigorous ‘right to work’ checks, but sophisticated counterfeit documentation was used in order to pass these checks,” Byron said, adding that it had a “legal obligation” to co-operate with the Home Office’s investigation.

The Metropolitan Police are asking anyone who recognizes the men suspected of releasing the insects to come forward.