There are some exemptions, mostly for salaried workers.

https://www.dol.gov/agencies/whd/fact-sheets/17a-overtime

The FLSA requires that most employees in the United States be paid at least the federal minimum wage for all hours worked and overtime pay at not less than time and one-half the regular rate of pay for all hours worked over 40 hours in a workweek.

However, Section 13(a)(1) of the FLSA provides an exemption from both minimum wage and overtime pay for employees employed as bona fide executive, administrative, professional and outside sales employees. Section 13(a)(1) and Section 13(a)(17) also exempt certain computer employees. To qualify for exemption, employees generally must meet certain tests regarding their job duties and be paid on a salary basis at not less than $684* per week.

Some industries (like mine) have mandatory overtime, but workers are absolutely compensated for that overtime.

The UAW is one of the most powerful unions in the US, so I'm not sure exactly where this post is coming from (as in, what specifically they are chasing via union action in this post), but from the context of other news it sounds like they're wanting similar comp without mandatory overtime in their industry.