Advice needed! I purchased a small office building in Oct 2019 with two tenants. One tenant is a small pharmacy who signed a 5-year NNN lease starting March 2019. According to the lease, the tenant pays a base rent plus estimated CAM charge each month. At the end of each year, the landlord provides a summary of actual CAM charges and invoices the tenant for any outstanding balance. The monthly CAM payment can also be adjusted at the landlord's discretion. In addition, the lease says that the base rent increases by $100 every 12 months. This is all very clearly written in the lease.

In December I sent a letter telling the tenant that the monthly CAM payment will be increasing from $620 to $780 per month as the 2020 budget shows a substantial shortfall.  The tenant did not respond to the emails so I tried repeatedly to call and finally only got ahold of her by calling from a different number.  She was very upset at me for “raising the rent” and said that her business is not doing well and she can’t pay the additional amount.  She acted shocked about the base rent increase and the additional CAM charges.  She said she will only pay the amount she was paying previously and no more. 

Any advice what to do?  Should I try to negotiate with her, or lay down the law and tell her to pay or get out?