Strike action at United Natural Foods continued into a second day as the union behind the action warned the US food distributor's investors the company's labour practices was putting the business "at risk".

UNFI, which supplies natural and organic food to retailers across the US, has seen staff at a distribution site in Washington state hold industrial action amid claims the company will not hold talks on pay.

The strike at the facility in Auburn started on Tuesday (11 December) and the walkout continued into yesterday. The Teamsters union claims UNFI has been unwilling to discuss the "huge compensation gap" between its staff and other grocery distributors in the area. Teamsters has also accused UNFI of other "unlawful actions", including worker surveillance and intimidation.

The union yesterday held a conference call with UNFI investors and analysts to report on what it said were "unsustainable labour practices" that were "jeopardising the company's operations".

Teamsters official Steve Vairma said: "UNFI management is risking its business across the country by provoking its workers into an unfair labor practices strike. The Teamsters will be notifying customers nationwide regarding UNFI's abuses."

The International Labor Rights Forum claim UNFI has made "serious violations" of global labour regulations, including threats and discrimination.

After day one of the strike, UNFI said it was "surprised and disappointed" at the industrial action.

"UNFI offered to return to the bargaining table as recently as yesterday, yet the union elected to go out on strike," it said.

It also brushed off Teamsters' claims of "unfair labour practices". The distributor added: "To date, the National Labor Relations Board has not found any instances of UNFI committing unfair labor practices, although the NLRB did find that the Union threatened UNFI's employees with loss of employment if they crossed the Union's picket line. The union continues to misrepresent the situation and undertake a smear campaign in an effort to damage UNFI's reputation.

"Given the union's decision to go out on strike during this busy holiday season, UNFI has no choice but to move forward with contingency plans, which include hiring replacement workers to support customers in the region."