The popular couple have apparently told producers that the new series, which starts on ITV2 tonight, will be their last as they plan to film a spinoff.
Their exit would leave few original stars on the programme following the departures of Mark Wright, Amy Childs and Lydia Bright. Bosses are said to be "desperate to find new stars to keep the show alive".
An insider told the Sunday Mirror: "This is the last thing we needed. Sam is the most popular female on TOWIE, one of the few original cast.
"She's had many offers but didn't feel ready to take that leap till now. Her relationship with Joey is one of the main storylines and he's agreed to take that leap with her.
"During the break from filming, Sam made a pilot for the spinoff. It concentrates on her relationship with Joey and all the joy and drama that entails.
"An announcement of which network will show it is imminent. There hasn't been a big TV couple since Katie Price and Peter Andre and Joey and Sam are keen to fill the gap."
Cara Kilbey has also quit The Only Way Is Essex. The show has suffered a drop in ratings in recent series and was savaged by critics for its live episode.