I mean what exactly does it mean? It's obviously not income related, you'll hear of unionized auto or other industry workers or people who work in oil extraction who make at least $50k/year if their jobs are still around described as "working class" but you'll never hear it for urban youngs who likely work service industry or low level office jobs and barely make over $30k if even that.
The new term for low-paid workers, whatever the collar, is "working poor" -- which includes checker-cashiers at stores, fast-food workers, low-level office clerks, cleaners, and domestic servants. Such people are easily atomized. They often are involved in no formal organizations, and they have no political allies.