Check out the companies making headlines in midday trading. 

AT&T, Discovery — The pair of stocks were volatile on Monday after the company’s announced a $43 billion deal to merge Discovery and AT&T’s WarnerMedia unit. Discovery’s A shares popped at the open but were down 3.8% in midday trading. AT&T was up about 1% but off of session highs. Before the official announcement, Citi praised the move and upgraded Discovery to buy.

At Home Group — Shares of the home furnishing retailer jumped 2.9% after the company’s largest shareholder CAS Investment Partners said it will oppose the deal to sell the firm to private equity firm Hellman & Friedman for $2.4 billion, the Wall Street Journal reported. CAS Investment Partners, which owns about 17% of At Home Group, said the bid “grossly undervalues” the company.

Marathon Petroleum — The energy stock jumped more than 2% after the company announced a modified Dutch auction tender offer for up to $4 billion of its common shares. Meanwhile, top Federal Trade Commission officials said Marathon Petroleum’s sale of Speedway gas stations to the parent of the 7-11 chain may be illegal on competitive grounds. The $21 billion deal closed on Friday, but the officials say they will continue to investigate.

Tesla — Shares of Tesla, down 27% over the last three months, shed 2.4% in midday trading after CEO Elon Musk said the company has not sold any bitcoin. Some investors had wondered whether the electric car maker had trimmed its bitcoin holdings after Tesla decided to stop taking bitcoin for automobile purchases.

Hostess Brands — Shares of the Twinkie-maker dropped 1.7% despite beating on the top and bottom lines of its quarterly results. Hostess Brands reported earnings of 20 cents per share on revenue of $265 million. Analysts expected earnings of 19 cents per share on revenue of $258 million, according to Refinitiv.

MicroStrategy — MicroStrategy tumbled nearly 9% amid a slide in the price of bitcoin to the lowest level in more than three months. The business analytics company holds roughly $5 billion worth of bitcoin. Bitcoin was last seen down 3.7% at $43,775, according to Coin Metrics.

– CNBC’s Jesse Pound, Maggie Fitzgerald, and Yun Li contributed reporting.