Tempur Sealy International, which manufactures Tempur Pedic and Sealy brand mattresses, has terminated its contract with Mattress Firm Holdings Corp, which operates 3,500 stores in 49 states under its namesake banner as well as Sleepy’s, after the retailer called for changes in the contract between the two parties. Tempur Sealy shares fell 29 percent on the news that it had reached an impasse with a trading partner that represents 20 percent of its sales.