The SURE lease explicitly states that Lessee is responsible for any severance taxes. If CHK is deducting them they are in breach of the lease (IANAL but this is a no brainer). Quoting directly from the lease (note the last sentence):

8.         Ad Valorem Taxes

            Lessee shall pay all Ad Valorem taxes or assessment of Lease Products or Lease Product reserves made by any local, state or federal entity or governmental unit attributable to, or resulting from the assessment of Lease Products from the Leased Premises regardless of the percentage of royalty paid to Lessor.  Lessee shall, in addition, pay any and all severance taxes or other excise taxes arising out of or relating to this Lease and/or the Lease Products.