(Reuters) -Long-term Starbucks ( SBUX ) shareholders have written to the company to resume talks with its workers union to discuss staffing, wages and other issues, a letter posted Thursday on the New York City Comptroller's website showed.

The letter, signed by Comptroller Brad Lander, Trillium Asset Management, the Shareholder Association for Research and Education and Pensions Investment Research Consultants, was addressed to Starbucks' ( SBUX ) board members Jorgen Vig Knudstorpand and Beth Ford and called on the company to reach a contract agreement with Starbucks Workers United.

"We are concerned that Starbucks' ( SBUX ) labor relations have significantly deteriorated, as reflected by over one hundred Unfair Labor Practice complaints filed since the beginning of the year, in-store actions, partner walkouts and protests over store closings, and even strikes," the letter said.

Starbucks ( SBUX ) did not respond to a request for comment outside regular business hours.

The union has been at odds with management for months. Talks between Starbucks ( SBUX ) and Starbucks Workers United, which represents more than 12,000 baristas, began in April last year but have since stalled.

In December, union members staged multi-day strikes across several U.S. cities during the peak holiday season.

"Over three years have passed since the first successful union election by Starbucks Workers United and yet no contract agreement has been reached," the letter said.

The Starbucks' ( SBUX ) store in Buffalo, New York was the first company-owned location to unionize in the U.S. in December 2021.

There are over 650 unionized Starbucks ( SBUX ) stores currently in the country, according to the SBWU's website.

The SBWU republished excerpts from the shareholder letter on its website, without commenting further.

Last month, Starbucks ( SBUX ) said it would shutter underperforming stores in North America, including its flagship unionized outlet in Seattle, as CEO Brian Niccol pushed ahead with a $1 billion restructuring aimed at reviving sales.