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."