One party to a lease cannot change the terms unilaterally. A lease can be changed, but only if both parties agree. Each party must give the other something in exchange for the other's promise, and then it will be enforceable.
With that said, if you're leasing the trucks from him, he currently doesn't have any legal right to be involved in your business as long as you're paying him. There is no need to change the lease, because he's already not allowed to do what he's doing. One option is to send a copy of the lease agreement to the company, along with a letter explaining that you have sole authority and asking that they refuse to speak to this man about them. Another option is to send him a "cease and desist
" letter, explaining that there is a tort
that prevents the intentional interference with contracts and that you will sue for him damages if he does not stop trying to involve himself in matters where he has no legal right to do so. If necessary, having a local attorney draft the letter for you may cause him to give it more attention than if it comes from you.
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