Marshall had said before last Thursday's game he was wearing the shoes to attract attention to Mental Health Awareness Week. Marshall has been treated for a personality disorder in the past.
Marshall posted the league letter informing him of the fine on Twitter and wrote: "Football is my platform not my purpose. This fine is nothing compared to the conversation started & awareness raised."
Marshall said he had planned to match any fine with a donation to his foundation, which supports mental health awareness. He said he also plans to auction off the shoes and donate the proceeds to charity.
Copyright 2013 by The Associated Press