Since when brokers withhold money for taxes?
Their only job is to provide forms for you to file. Something ain't right with this story
I had a similar request a few years ago.
My bank ( European bank!) asked me information (beneficial ownership) to avoid that the bank would be responsible for the taxes that might be due in the US. The US can present the bank huge claims. Banks are responsible for their clients. Deloitte did what was needed to solve the problem.
