BEIJING (AP) — Police beat workers protesting over a pay dispute at the biggest factory for Apple’s iPhone, whose new model is delayed by controls imposed as China tries to contain a surge in COVID-19 cases.

Foxconn, the biggest contract assembler of smartphones and other electronics, is struggling to fill orders for the iPhone 14 after thousands of employees walked away from the factory in the central city of Zhengzhou last month following complaints about unsafe working conditions.

China’s status as an export powerhouse is based on factories such as Foxconn’s that assemble the world’s consumer electronics, toys and other goods.

The ruling Communist Party is trying to contain the latest wave of outbreaks without shutting down factories and the rest of its economy as it did in early 2020. Its tactics include “closed-loop management,” under which workers live in their factories with no outside contact.

Foxconn offered higher pay to attract more workers to the Zhengzhou factory to assemble the iPhone 14, which sells starting at $799 in the United States.

On Tuesday, a protest erupted after employees who had traveled long distances to take jobs at the factory complained that the company changed terms of their pay, according to an employee, Li Sanshan.

Li said he quit a catering job when he saw an advertisement promising 25,000 yuan ($3,500) for two months of work. That would be a significant hike over average pay for this type of work in the area.

After employees arrived, the company said they had to work two additional months at lower pay to receive the 25,000 yuan, according to Li.

“Foxconn released very tempting recruiting offers, and workers from all parts of the country came, only to find they were being made fools of,” he said.

Videos online showed thousands of people in masks facing rows of police in white protective suits with plastic riot shields. Police kicked and hit a protester with clubs after he grabbed a metal pole that had been used to strike him. People who shot the footage said it was filmed at the site.

The protests in Zhengzhou come as the ruling Communist Party faces rising frustration about restrictions in areas across China that have closed shops and offices and confined millions of people to their homes.

That has boiled over into protests in some cities. Videos on social media show residents tearing down barricades set up to enforce neighbourhood closures.

The ruling party promised this month to try to reduce disruptions by shortening quarantines and making other changes. But the party is sticking to a “zero-COVID” strategy that aims to isolate every case while other governments relax controls and try to live with the virus.

The protest in Zhengzhou lasted through Wednesday morning as thousands of workers gathered outside dormitories and confronted factory security workers, according to Li.

Apple Inc did not immediately respond to a request for comment.

The company earlier warned iPhone 14 deliveries would be delayed after access to an industrial zone around the Zhengzhou factory, which Foxconn says employs 200,000 people, was suspended following outbreaks.

Other videos showed protesters spraying fire extinguishers toward police.