The General Rule: A Signed Lease Locks Both Sides In
A lease is a contract, and one basic rule of contract law is that neither side can unilaterally rewrite it once it's signed. A written lease is generally only modified by another written agreement, an oral agreement that both sides actually carry out, or new consideration exchanged for the change — not by one side simply announcing a new rule (Cal. Civ. Code § 1698). That means during a fixed-term lease, a landlord posting a new "no grilling on balconies" notice or adding a rule about guest parking generally can't be enforced against you as a lease violation unless you agreed to it, your lease already gave the landlord that authority, or the new rule reflects a change in the law itself.
Why Month-to-Month Tenancies Work Differently
This changes once you're on a month-to-month (or other short periodic) tenancy rather than a fixed term. Because that kind of tenancy renews automatically at short intervals, some states let a landlord change its terms — rules included, not just rent — by giving proper written notice timed to a rental period. California's rule, for example, lets a landlord change the terms of a week-to-week or month-to-month tenancy with written notice, taking effect after at least 30 days for a month-to-month tenancy, with rent already accrued at the old rate up to the effective date (Cal. Civ. Code § 827(a)(1)). This mechanism exists specifically because a periodic tenancy doesn't lock in terms the way a fixed-term lease does — each renewal is a fresh opportunity for either side to propose changing terms going forward.
What a Landlord Can Usually Still Do Mid-Lease
Even during a fixed term, most leases include a "rules and regulations" or "house rules" addendum clause that lets the landlord update specific operational policies — pool hours, package room procedures, parking assignments — without renegotiating the whole lease. That's usually enforceable because you already agreed to it when you signed, as long as the change is the kind the clause actually covers and doesn't contradict a term stated elsewhere in the lease, like a parking spot you're specifically paying for.
A landlord can also always follow a change in the law itself — a new local ordinance about noise, smoking, or safety equipment applies regardless of what your lease says, and a landlord updating house rules to match it isn't really "changing the lease" in the way this question is about.
What Counts as an Improper Change
Watch for a new rule that actually changes something the lease specifically promised you — restricting a right the lease granted, adding a new recurring fee, or changing your use of the unit in a way the original lease didn't contemplate. A posted notice isn't the same as a lease amendment, and a landlord generally can't turn a posted notice into an enforceable lease term just by putting it on the door.
A Realistic Example
Say your fixed-term lease says nothing about parking because none is provided, and six months in, the landlord posts a notice that all residents must now pay $75 a month for an assigned spot or move their car off the property. That's a new recurring fee that was never part of what you agreed to — it isn't something a house-rules clause can typically create on its own, and unless your lease actually gives the landlord authority to add new charges like this, you're not on the hook for it just because a notice went up. Compare that to a notice reminding residents that quiet hours are 10 p.m. to 7 a.m., referencing a house-rules clause that was already in your lease when you signed — that's an operational detail, not a new obligation.
What to Do If New Rules Show Up
Read the new rule against your actual lease and the rules-and-regulations clause it's supposedly coming from — if it's outside what that clause covers, or contradicts something the lease specifically promised, you can point that out in writing rather than assuming you have to comply. If you're on a month-to-month tenancy and got a formal notice of changed terms, check that the notice met your state's timing and delivery requirements before assuming it's already in effect.
Honestkey™ reads an uploaded lease and tells you what your rules-and-regulations clause actually allows a landlord to change without your separate agreement.