Check out the companies making headlines after the bell Monday:
Mattress Firm popped after announcing it agreed to buy HMK Mattress Holdings, the owner of mattress retailer Sleepy's, for about $780 million. The deal will give Mattress Firm over 1,050 stores in 17 states in the Northeast U.S, New England, the Mid-Atlantic and Illinois.
El Pollo Loco, the Mexican-style restaurant chain, surged on a positive note by Guggenheim Securities analyst Matthew DiFrisco. But shares of Wingstop were slightly lower despite a buy rating from the same analyst.
Shares of American Airlines dipped after it said that members of the association representing its reservations and gate agents had approved a new five-year contract that includes "immediate and significant pay raises."
Aluminum producer Alcoa inched higher after a Reuters report surfaced claiming an unnamed aluminum producer had offered Japanese buyers a premium of $120 per ton for January-March primary metal shipments, up 33 percent from the previous quarter. Negotiations include Alcoa, Rio Tinto and South32, the report added.
AT&T got a small boost after it confirmed that it plans to increase the price of grandfathered unlimited plans in February. "Our unlimited data plan customers continue to receive an incredible value, especially those taking advantage of our 4G LTE network," the company told CNBC.
Global chemistry company, Chemours, was up after it announced three auctions related to its transformation plan.
— Reuters contributed to this report.