Jason Aldean's using his "Saturday Night Live" opener after the deadly Las Vegas shooting -- a powerful cover of Tom Petty's "I Won't Back Down -- to raise money for the victims ... TMZ has learned.
The track's available Friday across many digital retailers and streaming services, and will continue to be released on more channels the next few days. Jason also has released "We Won't Back Down" t-shirts for $35. All proceeds will go toward the Direct Impact Fund to benefit victims of the massacre.
As you'll recall ... Aldean appeared on 'SNL' and delivered a defiant message of unity and resolve just days after he was onstage at the Route 91 Harvest Festival near Mandalay Bay when Stephen Paddock attacked.