UNISON has accused a Labour-run council of using illegal strike-breaking tactics in their long-running action to receive the same pay retention bonus as their colleagues in children’s services.

Mental health workers are due to begin the next phase of their strike action at Barnet Council in north London next Monday.

But a statement from the branch says the authority’s director of adult social care has informed members that he engaged the services of agency workers supplied by Flex 360 and that such a use of “agency workers by an employer during industrial action is unlawful.”

Last year the union defeated the government in the High Court, with judges ruling that legislation which allows employers to use agency workers to replace those on strike, was unlawful, unfair and irrational.

The union said it has written to the council’s chief executive to encourage the director to “withdraw from this ill-advised course of action,” saying that members “are furious at this crude attempt to bully and intimidate them only days before they begin nine weeks of strike action over a 13-week period.”

The mental health team has taken 27 days of strike action since September last year.

Branch secretary John Burgess said: “In 28 years of being a Barnet Unison rep I have never experienced the amount of anti-union rhetoric coming from senior management.

“Unison has reached out several times to offer to resolve the dispute only to be met with machismo-style management which has no place in the workplace and especially a workplace which is now a Labour-controlled council.

“My message to the council is stop the bullying and come back with an offer which our members would be prepared to accept.”

A Barnet Council spokesperson said: “We are not employing agency workers but are putting additional service provision in place from an external supplier, and this is in compliance with relevant legislation and guidance."