Linda McMahon was in the hot seat during a hearing in D.C. on Wednesday ... when a Republican congressman called her out and demanded answers ... about John Cena's engagement. 

The congressman pushing the issue is Rod Blum of Iowa -- who used his 45 seconds of floor time ask Linda about the big story from WrestleMania 33 ... Cena's proposal to Nikki Bella

The question got some chuckles in the room ... but one person who wasn't havin' it was Linda. 

The head of the Small Business Administration smiled ... but shut Blum down with the efficiency of a patented John Cena STFU.