I have no idea what the response will be, but when TASS reports it and cites a Foreign Ministry statement, this is no idle threat.
"We pointed out in this regard that if the transit of goods between the Kaliningrad region and the rest of Russia through Lithuania is not fully restored, Russia reserves the right to take action to protect its national interests," the ministry said in a statement after summoning Lithuania's Charge d Affaires Virginija Umbrasene.
Just as importantly, what will NATO's response be if there is a military confrontation over access?
Article V.