Mahtadi workers in Mumbai

I work in the interior design space in the city of Mumbai. Very often we have these people who say they are ‘Mahtadi’ workers and we have to pay them to unload and load the material delivered on our sites even if we don’t want them to do the job. We HAVE TO pay them regardless of whether they do the job or not. If we don’t, they don’t let the material reach our site. On top of this, they demand a certain amount of money. We can’t pay them how much we think is okay. For eg: one guy said to pay him 15k for unloading 3 vehicles. I do not know the rates. Please can someone tell me more about this. Some people say this is legal and is the law. Extortion in my opinion is illegal but open to what you guys have to say and / or if you’ve experienced this ordeal before. I am enraged. This is not fair to honest, hard working taxpayers of the country!