Arnoldo Bazan, 30, and Yini De La Torre, 19, both of Shawnee, are accused of mixing a Methomyl-based pesticide into the salsa.
Dozens of customers became ill, suffering from nausea, abdominal cramps, weakness, sweating and discomfort.
According to the indictment, Bazan claimed the owner of Mi Ranchito restaurants as responsible for him losing his job and his vehicle.
Prosecutors said the couple devised a plan to use the poison in hopes the owner would be blamed and suffer financial harm.
If convicted, the pair could face 20 years in prison and fines of $250,000.