The centre back, who received a second yellow card for kicking out at Ibrahima Konate in added time, did not immediately leave the field after being given his marching orders and argued with the referee, leading to the FA charging him for acting in an "improper" manner.
"The defender subsequently admitted the charge, and an independent regulatory commission has now imposed a one-match suspension and 50,000 pound after a hearing," the FA posted on X.
Romero, who served his automatic one-match suspension in Spurs' 1-0 win at Crystal Palace on December 28th, now faces an additional game on the sidelines.
With Spurs 14th in the table and winless in their last three games, Romero apologised to the club's fans in a social media post, suggesting it should not be the players having to front up to the supporters.
Spurs manager Thomas Frank said on Thursday that Romero was a "young leader" who made a mistake, and that he and the club's sporting director, Johan Lange, had met with him to discuss the post.
The North London club host Aston Villa in the FA Cup third round on Saturday.