Check out which companies are making headlines before the bell:
Canadian Pacific — The firm sent a revised takeover bid to Norfolk Southern, saying it is "financially more attractive and dramatically reduces the regulatory uncertainty for NS shareholders." Norfolk's board of directors unanimously voted against the initial offer.
Toll Brothers — The luxury homebuilder poster mixed quarterly results, with earnings per share coming in at 80 cents and revenue at $1.44 billion. Analysts polled by Reuters expected the company to report earnings per share of 83 cent on revenue of $1.43 billion.
AutoZone — The auto parts retailer reported better-than-expected earnings per share for its fiscal first quarter. The company also posted revenue that was in line with expectations.
H&R Block — The tax service firm posted a wider-than-expected quarterly loss on Monday. The company said its total revenue fell 4.6 percent amid foreign exchange headwinds.
Staples — BB&T downgraded shares of Staples to "hold" from "buy," citing concerns over the Federal Trade Commission's decision to challenge its merger with Office Depot.
Amazon — Pacific Crest initiated coverage of Amazon's stock with an "overweight" rating and an $800 price target. "We believe that Amazon's ecosystem aims (we think successfully) to be a part of the consumer's purchase process for most anything, making it one of the stickiest retailers."
FireEye — Citi upgraded FireEye's stock to "buy" from "neutral," citing its ability to grow quickly and "expand its product line into adjacent markets."
Comcast — Nomura Securities initiated coverage of the media giant with a "buy" rating and a price target of $72 a share, citing its content ownership, brand distribution infrastructure, "advanced X1 user interface technology," and low price-to-earnings multiple. (Disclosure: Comcast owns NBCUniversal, which is the parent company of CNBC.)
Home Depot — The retailer reaffirmed its 2015 forecast, saying it expects sales to increase about 5.7 percent for the year, with same-store sales up approximately 4.9 percent. The company also expects adjusted earnings per share to grow approximately 14 percent to $5.36.