An investigation is ongoing at the Iowa Fertilizer Plant in Wever, Iowa, after a note was found Monday afternoon indicating “a bomb will go off tomorrow at 12:00,” according to media reports.

The message was found Monday afternoon on the wall of a Porta Potty at the plant. No devices were found after police searched the plant and vehicles were searched as workers arrived to the plant.

After finding the bomb threat, the plant was evacuated so police could search the area.

Lee County Sheriff Jim Sholl said a 36-man safety team looked for suspicious items, but none were found.

“There are no gas storage tanks or other storage tanks containing any volatile or combustible materials,” Sholl said in a press release.

Iowa Fertilizer Company is constructing a fertilizer plant in Wever, Iowa, that is scheduled to open later in 2015. The $1.8 billion project has been considered controversial because the large tax breaks that were given to the company, which is owned by Orascom, an Egyptian company.

Although no suspicious items were found, the investigation is ongoing.