YNW Melly's attorneys are blasting the decision to keep him locked up as he awaits retrial in his double murder case ... and they're citing a recent ruling involving the alleged Trump attempted assassin.

Melly had his bond denied Thursday and his lawyers, Drew Findling and Carey Haughwout, ripped the decision in a statement to TMZ ... "The irony is that in the last few days, the nation saw a United States Magistrate Judge apologize to an individual accused of an attempted assassination of the President for his mere days in solitary confinement and not a word by this Court regarding the three years."

They're referencing Cole Allen ... a judge apologized to him in court for his jail condition.

His attorneys say YNW Melly -- legal name Jamell Demons -- has endured "inhumane conditions" behind bars for over seven years, including the last three in solitary confinement, as his case makes its way through the courts.  

Findling and Haughwout add ... "In the collective decades of experience shared by this defense team, we have never encountered such cruel treatment comparable to what Mr. Demons has endured. Numerous colleagues across the legal community have likewise expressed disbelief and outrage at the conditions imposed in this case."

YNW Melly's retrial is scheduled for January 2027 ... he's charged in the 2018 shooting deaths of two, Christopher Thomas Jr. and Anthony Williams.