Boston Mayor Marty Walsh is reportedly involved in a federal investigation into allegations of strong-arm tactics made by workers' unions, according to WCVB Boston.

The investigation reportedly aims to determine whether labor officials threatened building developers who hired nonunion workers to work on planned high-rise building projects.

According to the Boston Globe, investigators set up wiretaps and secretly listened to Mayor Walsh’s conversations with building developers in 2012. Walsh was the head of the Boston Building Trades from 2011 to 2013 before he resigned and decided to run for mayor.

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A spokesperson from the mayor’s office released an official statement stating that Mayor Walsh is a strong advocate for Boston workers and he’s always worked ethically when he was head of Boston Building Trades.

“Prior to running for mayor, Marty Walsh spent a little over two years working for the building trades advocating on behalf of working men and women in and around Boston," the statement said. "He is confident that he always acted ethically and appropriately in that role. Whatever broad review of labors activities that may be going on, it has little to do with the Walsh administration. The mayor will continue to make the necessary reforms in Boston to guarantee an open and inclusive development process."