Centre-back Shawcross was given a red card for a professional foul on Clint Dempsey, resulting in his second goal in a 2-0 win via a penalty, which ordinarily carries with it a one-match suspension. However, as it was Shawcross' second red card of the season it means he will now miss two matches.
Pulis told the club's official website: "To me, Dempsey looks like he is already on his way down before Ryan puts his arm around him. Even if you accept that it was a penalty, for the referee to then send him off adds insult to injury. What is particularly harsh is that we now lose him for another two matches, so the punishment doesn't fit the crime, and that really needs looking at."
Shawcross will sit out the FA Cup fourth-round tie at Wolves on Sunday, as well as the Barclays Premier League trip to Liverpool three days later.