The labor union for staff of Uber Technologies Inc.'s food delivery service in Japan called Thursday for the U.S. ride-hailing giant to reverse recent pay cuts and negotiate over working conditions.

The base pay of Uber Eats delivery staff in Tokyo was lowered late last month without a detailed explanation, the union said. The company, for example, slashed the base rate for a 5-kilometer delivery by about 22 percent to 621 yen ($5.7) from 793 yen.

The union has demanded a thorough explanation regarding the changed rates, but the company has not provided one, the union said.

"I cannot understand why Uber failed to talk with the union. We don't have any intension to attack the company," said Tomio Maeba, chairman of the union said at a press conference in Tokyo.

An Uber Japan spokeswoman said Thursday that "our delivery partners are not categorized as workers under the Japanese labor union law but independent contractors."

Uber and rival Lyft Inc. have drawn criticism for not providing their contracted staff with insurance for accident compensation and other benefits granted to regular workers. Uber has said it will introduce an injury compensation program in Japan.

Since the union was formed in October with 17 delivery staff, it has called on Uber's local units to negotiate on working conditions but they have rejected the request, according to the union.

"Uber's delivery staff are obviously company employees working under the labor union law from the viewpoint of legal precedents as they are completely working for Uber's business but without the right to reject the company's decisions regarding their contracts," said Yoshihiko Kawakami, a lawyer supporting the union.

The union and its lawyers plan to file a petition early next year with the office of the Tokyo metropolitan government in charge of arbitration in labor disputes, they said.

"This is our problem and also a global concern as Uber has caused labor trouble around the world," said Rikio Kozu, head of the Japanese Trade Union Confederation, known as Rengo, who also attended the press conference.

There are an estimated 15,000 Uber Eats delivery staff in Japan. They are directed by the company to pick up food and beverages at restaurants via the Uber Eats application.