Former Real Betis boss Setien indicated Barcelona have offered no compensation and said the Catalan club have failed to honor terms of the contract he signed in January.
In a statement that Setien posted on social media, from himself and his coaching team of Eder Sarabia, Jon Pascua and Fran Soto, it was claimed that all four only received written confirmation of their sackings on Wednesday of this week.
Those came via burofax, the coaches said, with the statement saying there had been "absolute silence on the part of the FC Barcelona board of directors" until that point.
According to the statement from Setien and his coaches, Barcelona indicated "a clear intention ... not to comply" with contracts that were signed on January 14, in the week that Setien succeeded Ernesto Valverde.
Setien said in the statement: "It is public and well known that, on August 17, both the club and the president announced my dismissal with immediate effect.
"However, it was not until yesterday, September 16 (one month later), when they sent me, for the first time, the written communication of said dismissal (without any settlement)."
The statement from Setien and his coaches added: "For all that has been said, we have been forced to put the conflict resolution in the hands of our lawyers, having to file the corresponding legal actions.
"This is in order to preserve our rights and what was agreed upon with FC Barcelona."
Setien endured a tough seven months as head coach after relacing Valverde.
Following a three-month pause in the season due to the COVID-19 pandemic, Barcelona were overtaken by Real Madrid in the LaLiga title run-in.
They were then humiliated 8-2 by Bayern Munich in the quarter-finals of the Champions League, a result which proved the final straw for president Josep Maria Bartomeu and the Barcelona board as Setien departed.
Captain Lionel Messi sought to follow his coach out of Camp Nou but could not agree terms for a free transfer.