JACKSON, Miss. (AP) — Nissan Motor Co. has declined U.S. State Department mediation of its dispute with the United Autoworkers over the union's attempts to organize a Mississippi plant.

The UAW says Nissan is intimidating workers at its Canton plant and violating their rights to unionize under international laws.

The UAW and the IndustriALL Global Union federation asked the State Department for mediation in April. That mediation could only happen if Nissan agreed, and the State Department announced Jan. 30 that the company had refused, saying it "regrets Nissan's unwillingness to participate in the process."

Justin Saia, a spokesman for the Japanese automaker, said Nissan prefers to rely on U.S. laws covering unionization.

"Nissan has declined to participate in mediation proceedings because long-established guidelines for bringing a union vote already exist as set forth by the National Labor Relations Board," Saia wrote.

The union appealed to the State Department as the American contact point for the multinational Organization for Economic Co-operation and Development. The organization has a code of conduct for multinational corporations.

It's the latest move in an ongoing struggle by the UAW to unionize the plant's 6,000 workers. No petition for a union election has been filed, but the UAW has been mounting an international campaign, in part because most non-American facilities of Nissan and its allied company Renault are unionized.

"It is clear Nissan behaves one way in some parts of the world but is grossly exploiting workers in the United States," UAW President Dennis Williams said in a statement. "The fact that the company continues to ignore the severity of the situation and its refusal to end these abuses or engage in dialogue that could result in a positive step forward for both workers and the company is absolutely unreasonable."

The automaker says respecting national laws is one of its core principles.

"Nissan respects labor laws in every nation where it operates and works to ensure that all employees are aware of these laws, understand their rights, enjoy the freedom to express their opinions and have the ability to select whether they wish to have external representation or self-represent," Saia wrote.

The State Department wrote that it "determined that the issues raised by UAW/IndustriALL are material and substantiated and merit further examination," but also said that if Nissan had chosen to mediate, that shouldn't be taken as an admission of guilt.

Nissan said the allegations were based solely on a UAW report.

The State Department recommended that Nissan conduct a company-wide review of labor rights and that it consider some kind of mediation with unions. The State Department said it had shared the information with OECD contact points in Nissan's home base of Japan, Renault's home base of France and the Netherlands, where the companies' alliance is incorporated.