Is it illegal to have a dog tied up everyday?

My sister in law has a small dog is always tied up they went on vacation and left the dog unattended. Of course my husband and I always check up on him make sure he has food and water. But the times that I have gone he cries or feels lonely. Idk I feel bad for the dog. And they never walk the dog. When they come back I feel like talking to her about it like why have a dog if it’s going to be unattended and just be tied up? Even though it’s none of my business. But I’m going to talk to her. I don’t understand why people have pets if they’re not going to treat them as family 😒