Treasury Secretary Steven Mnuchin led a "check-in" call Monday with President 's Working Group on Financial Markets, as stocks slid further down and a government shutdown continued with no immediate end in sight.

The Christmas Eve call with the group, which has been referred to as the "Plunge Protection Team," was scheduled to discuss coordinating agencies' functions during the shutdown, a senior administration official told CNBC. Members of the Federal Reserve, the Securities and Exchange Commission and the Commodity Futures Trading Commission participated in the call.

The call followed a series of moves by Mnuchin over the weekend aimed at reassuring markets. He also attempted to convey that Trump knows he does not have the authority to fire Federal Reserve Chairman Jerome Powell, whom the president has ripped while the central bank raises rates and equities markets sputter.