If any organisation wants to set a dress code, all they need to do is provide a uniform and make it a condition of employment to wear it. Simples.
Back when LATCC was still on North Side one of the ATCOs put in a claim for clothing damaged at work and requested a replacement item. He was issued with a long brown syoreman's coat.
Back in the 1960s word came down from on high in May/June that a summer dress code was in force, ties were no longer neccessary, sleeves could be rolled up and jackets hung over chairs. In the Autumn it was back to Civil Servant mode.
I remember one ATCA on the A side being admonished for his "slovenly appearance". The next daay he arrived in pin-stripe suit, bowler hat and rolled umbrella with a copy of the FT under his arm.
I can't remember ever hearing of a dress code anywhere but in NATS. It doesn't make better controllers, if people are comfortable they perform better. We had a rage for Hawiaan shirts one summer, brightened the Ops Room up no end