Full-line forcing is a method of marketing whereby the producer only ties up with a dealer if the dealer takes some or all of its range of products.
In this method, the supplier wants the distributors to carry their entire range of products even if they aren't necessary or beneficial to them. It can often be forced upon them and illegal for them to push the products as they do. If there is no reason for them to carry them, they can be illegal business pushing but if there is reason, it is not illegal.