I purchased a block of cheese from a store that sells both kosher and non-kosher cheeses. However, they cut the cheese with the same knife that they cut the non-kosher cheeses. Is this a problem?
There is a concern that a little bit of non-kosher cheese stuck to the knife and was transferred to your cheese. Therefore, you should remove a slice from where it was cut with that knife, and the rest of the block is fine.
Rabbi Shay Tahan