Given the brouhaha over the harmful effects of tobacco smoke, some landlords are writing lease and rental agreement clauses that prohibit smoking, either in the tenant's unit or even the entire building.

But it is quite a different animal to rewrite the rules or make them up smack dab in the middle of the lease. If the original tenant has a fixed-term lease, the landlord cannot change its terms until the lease expires. If that tenant rents month to month, the landlord can make a change after giving the tenant proper notice -- 30 days' worth, in most states.

Now, since you're a subtenant of a tenant with a lease, you must abide by the terms and conditions of the tenant's lease. For example, a no-pets clause in the lease would apply to you. But you also get to enjoy the rule about no changes mid-lease -- which means that the landlord can't insist that you stop smoking. Watch out, though -- if the tenant from whom you rent were to decide that he didn't want you to smoke in the apartment, he could give you proper notice (again, usually 30 days) and you'd have to comply.