There is no special law or anything covering it that I'm aware of, it's just that T-Mobile says "This will be a distraction, and there is serious risk that it won't happen. If you want us to take that risk, give us some insurance"
Apparently Sprint wants this deal badly enough to risk losing $1B if it doesn't go through, and T-Mobile was canny enough to realize this fact and negotiate for that clause in the contract.
There is no special law or anything covering it that I'm aware of, it's just that T-Mobile says "This will be a distraction, and there is serious risk that it won't happen. If you want us to take that risk, give us some insurance"
Apparently Sprint wants this deal badly enough to risk losing $1B if it doesn't go through, and T-Mobile was canny enough to realize this fact and negotiate for that clause in the contract.