Some Instacart shoppers and drivers, the people who buy and deliver groceries to the companies’ customers, have beefs about their compensation. Those grievances are bubbling over into a planned strike on Sunday and Monday.

The workers, who are independent contractors, are organizing on social media for what they’re calling a “no-delivery day.”

“We want to get Instacart’s attention,” said Jennell Lévêque, who’s worked for the grocery-delivery service in the Bay Area for 31/2 years. The workers want Instacart to highlight tipping for customers and to increase compensation for large and heavy orders.

While Lévêque and some other workers said the planned action would be national, Instacart said it only expected protests by a handful of workers in Austin, Texas, and St. Louis and did not expect any service interruptions.

Instacart said it already notifies customers prominently of the option to tip. It said workers already can decline orders without retaliation, or can call a help line to have the delivery fee increased or request a second person to assist them. Workers said they could be dinged if they decline too many orders and said it’s hard to reach the support line.

Instacart, a 5-year-old San Francisco startup, is valued at $3.4 billion. It operates in 154 U.S. cities and said it has hundreds of thousands of workers. The protesting workers said their main nexus is a Facebook group with 5,200 members.

“We realistically understand that we won’t shut down the company,” said Matthew Telles, who has worked as an Instacart shopper for two years in Chicago. “The nature of the job is that we are all separate, and not everyone is on Facebook. There will still be a decent number of people shopping” on behalf of Instacart customers.

That disparate work model has hindered other efforts by gig economy workers to organize. As independent contractors, they are barred by federal law from formal unionization. Uber drivers, the largest and most vocal group of gig workers, have held scattered protests.

Veena Dubal, an associate professor at UC Hastings College of the Law who studies Uber drivers and other gig workers, said several factors hinder organizing. “Casual workers have different and sometimes conflicting interests with full-time workers,” often because they need the freedom and flexibility to work part time, she said. Moreover, gig workers move on quickly to other jobs. “Full-time workers who feel exploited are much more likely to engage in collective action,” she said.

Lawsuits have been one major avenue for gig workers to join forces. Those from many companies, including Instacart, have banded together into class-action suits seeking to be reclassified as employees. A suit against Instacart ended with the company agreeing to pay out $4.6 million and clarify its tipping feature to customers. That settlement is pending.

Amazon’s $13.7 billion acquisition of Whole Foods, one of Instacart’s biggest grocery-store partners, threw that relationship into question, as Amazon has its own logistics network, including Amazon Flex, which uses independent contractors for Prime Now deliveries. However, Instacart reportedly has four years remaining in its contract with Whole Foods.

Meanwhile, Instacart has said the Amazon-Whole Foods deal triggered a stampede of other grocers seeking to partner with it to combat Amazon’s threat.

Karyn and John Ellis of Woodside have ordered from Instacart for two or three years and make a point to always tip their delivery person. On Friday, when they called about an order gone astray, customer service told them (erroneously) that there was a sick-out happening, Karyn Ellis said.

“The gig economy seemed like a good idea at the time, but now that you have people who are dependent on it for their income, it doesn’t pay, it doesn’t provide security,” she said.

Carolyn Said is a San Francisco Chronicle staff writer. Email: csaid@sfchronicle.com Twitter: @csaid