A natural gas leak caused an explosion at the plant that killed three employees and injured dozens of others.
Damage to the factory caused production capabilities to be reduced by about 50 percent.
Company officials said it was a difficult, but necessary decision "to ensure the long-term health of our Slim Jim business."
"We hope that by giving two months notice, we will help ease the transition for those employees who will be affected," ConAgra Foods Communications Manager Dave Jackson said.
Officials said the decision regarding which employees would be laid off would be based on seniority and production needs under the union contract.
The company also announced Wednesday they would be returning to standard pay policies and would no longer give all employees guaranteed 40-hour weekly paychecks beginning the week of Sept. 21.
"We want to emphasize once again how important our employees have been in the recovery of this plant," Jackson said. "We recognize that many challenges and difficulties still lay ahead, but we are optimistic about the future of our Garner facility."
ConAgra currently employs about 750 employees at its plant in Garner.