If there is a written lease, then each party is obligated to do those things--but only those things--contained in the lease itself. Neither party may unilaterally (or without the agreement of the other) add any additional restrictions, obligations, etc. The only exception would be if the lease, by its terms, made reference to some external set of rules (e.g. house rules), which contain a parking restriction; or if the lease specifically gives the landlord the power to later enact certain rules. So from what you write, it would seem that the landlord could not add this parking restriction.Note, though, that if the area is one in which it's illegal to park in for other reasons--e.g. it's blocking the entrance to a garage or parking lot; it's a no-parking zone generally; etc.--then you could not park there.