N.H. Rev. Stat. Ann. § 378:36

If the public utilities affected thereby shall fail to agree upon the division or apportionment thereof, the commission may prescribe the division of such joint rates, fares, charges and classifications between such public utilities and may revise any division agreed upon which shall be found inconsistent with the public interest. In making such apportionment, the commission shall consider the financial impact of the apportionment on each utility affected by such apportionment.