New Landlord Saying My Current Lease Is Expired And Is Telling Me To Sign His New One Or Leave

Location: Illinois

Signed a 12 month lease from December 2025-2026 in June, new landlord bought the building around August and until now he gave everybody in my building a packet stating:

“ I appreciate your tenancy. Your lease has expired. Due to general cost increases and to match existing market conditions, I am increasing your rent. This letter formally advises you that your rent will increase to X per month effective 03/01/2026.

This increase does not affect any other obligation under your lease. For example, your rent due date will remain the same.

Thank you for understanding the cost pressures on me as I understand those on yourself. I appreciate your tenancy and hope you will continue to remain for a long time.

Enclosed is two copies of your new lease. Please sign and date both and return one to me. You can leave the signed lease in the dropbox outside the building at if you wish to renew your tenancy at the new rate, you may do so by paying rent at the updated amount beginning on the effective date above.

If you do not wish to renew your tenancy at the new rate you must vacate the unit. I am serving this Notice at least 30 days before the end of your month to month lease term so you have time to move out. If you do not move out by the time your lease ends, I will file a lawsuit to evict you. In the meantime, you must still pay the rent you owe and follow the other terms of your lease.”

Is this even legal? I dont think so and not entirely sure of my next step . TIA

Edit: I also texted him this: hi landlord I want to clarify that I have a valid 12-month lease that runs through December 2026, which transferred to you when the property was sold. And not on a month to month nor expired lease. I’m happy to continue under the current lease terms. Please confirm you’ll be honoring the lease as written. Thanks. He responded :

no. Your lease is not valid because it's effective date is after the date that I purchased the building. It's a post dated lease.