Is it with whomever or with whoever?

Choosing whoever or whomever can be easy. Whomever is an object pronoun and works like the pronouns him, her, and them (Give the document to whomever in the department). Whoever is a subject pronoun and works like the pronouns he, she, and they (Whoever wrote this poem should win a prize).

Can you say with whomever is?

Like who and whom, the trick to telling whoever and whomever apart is the letter M. Both him and whomever are object pronouns and have M’s in them. If you can replace the word whomever with him, you’ve used it correctly. If you need to use he (a subject pronoun) to make the sentence correct, you should use whoever.