Jay-Z's increasing his calls for a court to sanction Tony Buzbee -- the lawyer representing numerous people accusing Diddy of a variety of sexual misdeeds -- with Jay's side blasting him for not even meeting with his client before he filed the complaint ... but Buzbee isn't backing down.

The rapper's new legal docs in support of his motion were filed earlier this month asking for sanctions against Buzbee ... and, in it, Jay's team points out that Tony now admits he never met with the Jane Doe suing him before he signed off on the complaint.

Although Buzbee insists the case was appropriately vetted, Jay's lawyers are hammering him for never actually meeting the Jane Doe before it was filed -- which Jay and his side see as a huge lapse in his ethical responsibility.

As you know ... Buzbee's working with a ton of different clients right now, so it's not totally shocking he hadn't met this particular Jane Doe before -- but, he's still catching flak over it from Jay's side.

Jay-Z's team wants the court to sanction Buzbee, claiming he didn't do the bare minimum to investigate his client's claims before she gave a now-infamous NBC interview.

Not long after the interview aired, the subject of it admitted there were certain "mistakes" she made while recounting her story.

Buzbee tells TMZ this reply to the lawsuit is "weak and desperate," stating he did, in fact, personally interview the plaintiff, as did four other lawyers. Tony adds anyone who says otherwise has their own agenda.