Companies to Watch: T-Mobile joins S&P 500, Tesla to ramp up production, Marriott faces lawsuit

Here are the companies Yahoo Finance is watching today.

T-Mobile (TMUS) is joining the S&P 500. The cell phone carrier has been picked to replace Red Hat in the index starting next week. That's because Red Hat is no longer publicly traded now that IBM has officially acquired the company.

Tesla (TSLA) is getting ready to ramp up production. An internal email says it is "making preparations" to boost output at the Tesla plant in Fremont, California. No other details were released. Tesla delivered a record number of cars in the second quarter, and Elon Musk is known to set ambitious production goals.

Marriott (MAR) is facing a lawsuit over allegations of deceptive pricing. Washington, D.C.'s Attorney General says the hotel giant tacked hidden fees onto hotel bills. Sometimes the fees were grouped in alongside taxes and not disclosed until after customers entered their credit card information. Marriott is not commenting because of pending litigation.

GlaxoSmithKline (GSK) and Pfizer (PFE) just finished up a positive trial for their HIV treatment. The companies announced that they met their goals in a phase 3 clinical trial after their two-drug regiments showed an ability to control HIV in patients. The study was conducted to see if adults living with HIV on a three drug regiment could do so with a two drug plan.

Jay-Z is breaking into the pot industry after becoming the top brand strategist for the California cannabis firm Caliva. The company says the hip-hop mogul is set to play a critical role in its creative direction and will focus on outreach to “citizens returning from incarceration.” No word yet on any financial terms of the partnership.