Hell on Wheels may be spinning its wheels for a little while. John Shiban, the showrunner of AMC’s birth-of-the-transcontinental railroad drama, has stepped down, prompting the network to put Monday’s third-season renewal on hold, at least temporarily, while it searches for his replacement.

Here is the statement from AMC, and Entertainment One and Endemol, which produce the show: “John Shiban has informed AMC, Entertainment One and Endemol that while he was fully on board when the network informed him about their intent to pick up Hell on Wheels, he has since made the personal decision that he will be unable to return as showrunner. He has asked the production partners to seek a replacement showrunner. Like all of our shows, network pick-ups are always conditioned on an approved showrunner. We are confident that eOne and Endemol will satisfy that obligation in the near future.”

“I’m very proud of our work on Hell on Wheels and was thrilled to hear the show would have a Season Three,” Shiban said via statement. “I have since made the difficult decision that the time has come for me to leave. I care deeply about the series and will do whatever I can to aid in the transition to ensure the continued success of the show. I truly value all the time I have spent with this wonderful group of very talented people.”

Shiban, an executive producer of the series, was elevated to showrunner before season 2. Creators/executive producers Joe and Tony Gayton will not be involved in the day-to-day operations of season 3, but will serve in consulting roles.