Rent Increase Question

[Pedro Leon]

Good day,

So my mother in-law owns a duplex in Cape Coral, Fl. She lives in one side and rents out the other. The place is paid off. She has been renting out the other side of the house to the same tenants for 6 years at a massive discounted rate with no lease. I am working on drafting up a lease for her to give them. Are there any restrictions for the amount you can raise the rent? I'm not concerned with them deciding to move out if the number is too high. Looking at just getting it back to market rate because we are looking to rent out both sides within the next year.

Appreciate any thoughts!
Pedro