Stocks making the biggest moves midday: General Motors, Stellantis, Planet Fitness, Adobe and more

cnbc.com:

Check out the companies making headlines in midday trading.

General Motors, Ford, Stellantis — Shares of Ford rose slightly, while General Motors gained 1% and Stellantis was up 2% as a targeted strike by the United Auto Workers began. Workers walked off the job at several assembly plants belonging to the three automakers Thursday night after a key deadline to settle a new labor contract passed.

Planet Fitness — Shares slid 13% after the gym chain's board pushed out CEO Chris Rondeau. The move was shocking to employees close to Rondeau, a person familiar with the matter told CNBC. Board member Craig Benson, known for his role as the former governor of New Hampshire, is the interim CEO.

Nucor — The steelmaker fell 5% after offering worse-than-expected guidance for third-quarter earnings, with the company pointing to pricing and volume challenges. Nucor said to expect earnings between $4.10 and $4.20 per share, while analysts polled by LSEG, formerly known as Refinitiv, forecast $4.57.

PTC Therapeutics — The therapeutics stock plummeted 28.3% after the European Medicines Agency's Committee for Medicinal Products for Human Use issued a negative opinion on a conversion of conditional to full marketing authorization for a PTC drug to treat nonsense mutation Duchenne muscular dystrophy. Raymond James downgraded the stock to underperform from outperform following the news.

Core & Main — The infrastructure stock retreated more than 3% a day after it announced a secondary stock offering. The offering of 18 million Class A shares by selling shareholders will be held concurrently with the repurchase of 3.1 million Class A shares. Partnership interests in a company unit also will be bought back.

Arm Holdings — Shares slipped as