Q. What happens if one uses (dishes or utensils) that were not toveled (immersed in a mikva)?
Can you eat the food?

A. According to Tosafos (Avoda Zara 75b – d’h vechulan) it is a Tannaic dispute in the Talmud (ibid.) if after the fact of someone cooking or using non-immersed utensils, the contained food becomes prohibited rabbinically, as a measure of precaution for avoiding the usage of all non-kosher utensils. Some authorities maintain that it may even be a biblical injunction (Or Zarua 293 and others)
Halacha follows the opinion that it is permitted (Rema Y.D. 120: 16) Yabia Omer (Y.D. 2) rules that although the food is permitted, it should be removed immediately from the non-toveled container

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a