Michael Mandel hits another home run, this time with an excellent analysis of the relocation clause typically found in leases and suggestions for tenants in negotiating the clause.
This clause gives the landlord the right to move a tenant within the building (or sometimes even to another comparable building, which I would fight hard if presented to me) if the landlord gives adequate notice, pays expenses, etc.
Scary? Well, it does not happen very often, usually only to accommodate a major tenant in the building. I agree 100% with Michael, especially when it comes to floor and light and that the tenant should never pay more money or have its pro rata share increased by reason of the move. (However, if the new premises are smaller the numbers should decrease.)
I would add only one other point to consider negotiating: try to limit the number of times the tenant can be relocated.