When Vanessa Bain quit her job working with special needs students at a public high school in Silicon Valley to become a shopper for online grocery delivery company Instacart, she was wary of tying herself to a tech start-up that relied on contractors to meet demand, with little worker protection.

But Bain, then a 30-year-old mother, was quickly won over with meaningful work and a sense of respect. And her take-home pay rose roughly 65 percent compared to teaching and tutoring combined. At the end of a day working for Instacart, Bain had more energy, which made her a better mom. When a friend who drove for Lyft complained about pay cuts, Bain urged her to switch to Instacart.

That changed just a few months later, after Instacart in 2016 began a pattern of experimenting with worker pay in ways that made earnings more precarious. That included using tips to supplement wages, a practice the company stopped in February after public outcry.