A group of Whole Foods employees stepped up efforts to unionize the grocery chain in an email blasted to thousands of workers Thursday, citing a laundry list of grievances stemming from Amazon's purchase of the company last year.

The group set up a forum on messaging app Slack called Whole Worker that allows members to anonymously share their concerns about the company "without fear of losing their job," according to a copy of the email obtained by CNBC.

"In the last three years, we have experienced layoffs, job consolidations, reduced labor budgets, poor wage growth, and constantly being asked to do more with less resources and now with less compensation," the email said. "Jeff Bezos should not have earned 150 billion dollars while the majority of his workers live paycheck to paycheck and do not receive profit sharing."

One of their chief complaints is that Whole Foods reportedly stopped granting stock options to lower-level employees after Amazon's acquisition last year. They are fighting for better pay, benefits and profit sharing, according to the email.

The Wall Street Journal reported the latest effort to unionize earlier Thursday.

Betsy Harden, a spokeswoman for Whole Foods, said the company believes its wages and benefits are competitive with the rest of the market. She also pushed back on the need for a labor union.

"We respect the individual rights of our team members and have an open-door policy that encourages team members to bring their comments, questions and concerns directly to their team leaders," she said in an emailed statement. "We believe this direct connection is the most effective way to understand and respond to the needs of our workforce and creates an atmosphere that fosters open communication and empowerment."

Amazon didn't immediately return emails for comment.

The Retail, Wholesale and Department Store Union is helping to organize employees.

"The RWDSU stands with workers in precarious positions no matter what -- Amazon and Whole Foods workers are no different," union President Stuart Appelbaum said in a statement. "Part-time workers who cannot get enough hours to make an income above the poverty line; single parents who work two and three jobs to make ends meet and young workers who face extreme heath and safety risks that will debilitate them for life all need a union voice."

The New York-based labor union has about 100,000 members across the country.