The Coalition for a Sustainable Food Supply Chain said United Natural Food Inc. CEO Steven Spinner refused to sign a pledge promising to stop marketing conventional food as “natural” and increase the sales of certified organic foods.

The group, which includes the International Brotherhood of Teamsters as well as organic food advocates and environmental organizations, presented Spinner with the pledge at UNFIs Southeast Tabletop Show in Orlando, Fla. last week. The company holds the annual conference for its top retailers.

Providence, R.I.-based UNFI is the nation’s largest distributor of natural, organic and specialty foods and personal care products. The company supplies goods to Whole Foods Market.

Teamsters and their coalition allies said they have been asking UNFI and Whole Foods to end what Teamsters call “practices of monopolization, marketing natural over organic foods and violating workers rights throughout the supply chain.”

But UNFI Chairman Michael Funk called the request “a continuation of a policy of harassment” because of the Teamsters’ inability to unionize UNFI and Whole Foods workers.

The pledge they asked Spinner to sign also included promises to adopt fair trade standards that allow workers to choose representation and engage in collective bargaining and to promote sustainability by eliminating business practices that accelerate climate change.

“It is unfortunate that Steve Spinner speaks extensively about UNFI’s so-called sustainability commitment, but that he has not agreed to sign the pledge,” said John Williams, the Teamsters warehouse division director. “UNFI likes to talk the talk, but they also need to walk the walk.”

Teamsters also distributed leaflets to conference attendees that read, “What’s Gone Wrong at UNFI? Tell UNFI: Sign the Sustainable Food Chain Pledge Now.”

A UNFI spokeswoman said Spinner was traveling and could not be reached for comment.

But in a statement, UNFI Chairman Funk said: “This is just a continuation of a policy of harassment of UNFI and Whole Foods because of their inability to unionize the work force. Everyone in the natural products industry knows that over the last 35 years there has never been a stronger advocate of organic agriculture, fair trade items and products that benefit the environment than UNFI. If the teamsters are so concerned with climate change perhaps they should install solar panels at their headquarters, as UNFI has done."