Company codes assigned to a user not to a role

Hi -

We have set up our end user roles and now the requirement has come through that certain users should only have access to information based on company codes. Is there a way to assign a user to either 1 or several company codes, but not to all; and to not have to change all of the roles that she has access to?

Basically, assign a user to a specific company code, assign the necessary roles and have them only have access to that specific company codes information.

Thanks,

Margaret