Add System.Data to c# class file?

Can you add additional references to the c# class files you create through the BIMLExpress extension in Visual Studio?

I'm trying to add using System.Data to my class file and it is not recognizing it. 

But I can <#@ import namespace="System.Data" #> in my BIML file and it works just fine.

So how do I reference that same namespace from the C# class (.cs) file?

using System.Data?<br> &nbsp;