The workers’ complaints started to be picked up by news outlets including Fast Company and NBC. And they caught the attention of Working Washington, a union-backed labor group in Seattle, which collected more than 1,500 signatures of Instacart shoppers who objected to the company’s pay practices. Some began asking for cash tips outside the app, while others encouraged customers to leave 22-cent tips — a nominal amount meant to show solidarity with workers — through the app and then adjust the tips higher after a delivery was made.

On Wednesday, after the announcement that Instacart was changing its policies, a representative from Working Washington, Sage Wilson, said, “In the space of two weeks, Instacart workers came together, sparked a national media sensation and transformed the entire pay model of a $7 billion corporation.”

DoorDash, which is valued by investors at $4 billion, has not announced plans to change its tipping policy, which dates to 2017.

“DoorDash’s pay model provides transparency, consistency and predictability,” a company spokeswoman said on Tuesday. “Since implementing this pay model more than a year ago, we’ve seen a significant increase in dasher retention, percentage of on-time orders and dasher satisfaction.”

After Instacart’s announcement on Wednesday, the DoorDash spokeswoman declined to comment.

Many Instacart shoppers were thrilled by the company’s about-face. In a private Facebook group, some celebrated their successful campaign to get the company to change its tipping policy and make them whole on previous payments.

“I can’t believe it! Back pay!” one shopper wrote.

“THIS is why you stand up for yourself against corruption,” wrote another.

“I’m very excited that we got Instacart to listen to our complaints,” said Ashley Knudson, an Instacart shopper in Seattle. “I feel like we have some work to do, and we’re not going to back down until we get the consistency that we need in our batch payments. We consider this a small victory, for acknowledging their mistreatment, but we look forward to pushing onward and having our voices be heard.”