Poor friend's church requires 10% of their gross income given as tithe

I want to ask this group as a non-religious but concerned friend if this normal? My wife's friend comes from a poor family who don't really have any savings or funds for retirement. They budget and ration their food, but the church they attend requires them to give 10% of their total income as a tithe. They say it's commanded by the bible and all the churches do it. It sounds sketchy to me and I had never heard of this from other Christians. Is this legit?

Edit: Appreciate your thoughts, Christians. She's a young girl who newly moved into an expensive city, so I was concerned upon learning she resorted to no longer buying meat/eggs/milk to save money yet is paying hundreds of dollars for the tithe required by her congregation. I expect it may be a sensitive conversation to talk to someone about changing churches but I will gently bring up your biblical quotes and maybe open her mind to the thought of attending a different church.