Is my roommates small business legal?

Type and print a letter

"Notice to quit or vacate"
type something to the effect that it has come to the landlords attention that a tenant of (insert address) is operating a fitness training business out of the premise in violation to the residential use lease in addition to a number of local laws and ordinances. You have 3 days to remove the offending material and desist all nonresidential activities, Vacate the premise, or face legal eviction proceedings.

The next time he leaves the house....when he comes back....as a group...AMBUSH HIM WITH THIS LETTER...be irate....tell him his hustle is about to get you all kicked out and that you took a house vote and feel it is best that he finds other housing arrangements IMMEDIATELY. Lean heavy on the fact that YOU ALL arent going to have your credit and tenancy ruined by his BS.

/r/smallbusiness Thread