Rental agreement : hosting people

Me again !

I've got a question regarding rental agreement in general, not facing the situation (not yet, maybe).

In France, a landlord rents a property to a tenant, who is granted the right to do (almost) anything with it, the rule being that you must return the property in the same state as you received it. Thus, the landlord can not forbid you from hosting people (friends, family, the whole neighborhood if it fits into your flat :D).

How does it work here ? I'm asking as I have been hosting my brother for one month now. He's planning to stay, we hence decided to head to immigration directory where I was required to provide, not the rental agreement this time, but a letter from the landlord allowing him to stay here with me.
Does it mean that hosting can be restricted by landlords or is it only an additional precaution ? But I don't think so as they seemed to stick to the minimal required documents so far. I also thought it might be a requirement for foreigners. And conclusive question, my landlord is a good person, and will most likely not refuse, but what "if" ?

Give me your thoughts, and even better, the answer if you have it ;)
Thanks in advance.

In none of my rental contracts has there been anything limiting visitors or the number of people able to live in the home. That being said, when it comes to immigration issues, you will always need the OWNER of the property to give permission for an individual to live there.

For example- when I first moved here, I was staying with my husband's parents. They have been renting the same flat for about 30 years, but I still had to get a note from the owners that I was allowed to stay with them. Similarly, when my husband switched his temporary residence to Gabrovo (he is Bulgarian, btw) he had to have our landlord go to the obshtina to sign a form permitting him to live there since I was the one on the lease. (We had done the lease in my name for immigration purposes). So, in theory, your landlord COULD deny to fill out those papers, which would make it difficult (impossible) to do the correct immigration paperwork. But it is less of a "allowed to stay in the home" issue and more of a "legally taking responsibility for a renter" issue.

That being said, I have never had a landlord who would not either give me a notarized letter or go in and fill out the necessary paperwork.

Thank you Kojidae.
My landlord was surprised by me asking such a letter, as she just said that I could live with who ever I like. But she was nice and just signed me a letter which I had prepared before.
Note that I was told at the immigration office that they might indeed need a notarized letter and then it finally appeared that the one we had made by ourselves was enough.