Create a dependency when a certain Account is selected, another required field is required, when creating a Case

In our instance of Dynamics (2015, Online), when you create a Case, the Account/Customer field is required (tied to customerid) by the system. I was wondering if there was a way that if a certain Account (e.g. Company A) was selected, then another field becomes required by the system. However, for example, if Company B was selected, the additional field would not be required.