All of the chicken suppliers with whom the company has a direct relationship have already eliminated the use of human antibiotics as growth promoters in the chickens.
In formal writing, we try to avoid ending a clause, sentence or question with a preposition. However, it's very common and acceptable in speech to do so: 'All of the chicken suppliers whom the company has a direct relationship with have already eliminated the use of human antibiotics as growth promoters in the chickens.' In fact, people might find it snobbish if you use 'with whom' in speech.
Note that ending a clause, sentence or question with a preposition is not wrong.
Change these two sentences:
1. This is the school which I graduated from.
2. These are the friends whom I'll be travelling with.