Generally speaking, they will definitely read them (and occasionally take action), but only respond if they have some legal obligation to do so. Any reply they make to an inquiry or accusation of this type can be used against them, but a lack of response cannot (unless that lack of response violates some requirement of the law).

This is why it's good to have a bilateral contract with them prior to your contact, so that they have a legal obligation to reply. When they dont reply to your offer of renegotiation or relief, you're safe to use their silence as acquiescence or dishonor, depending on circumstance.