Around a dozen police barged into Wu Rongpu's apartment in the early hours and dragged away his labour activist wife, leaving their one-year-old daughter screaming.

"They came into the room and tore through everything they could" looking for evidence of Zhu Xiaomei's work for a small Chinese workers' rights organisation.

Last week, just over a month after she was detained, authorities formally arrested her on charges of "gathering a crowd to disturb social order," which carries a maximum sentence of seven years in jail.

Zhu, 36, came to Chinese authorities' attention for her role as a labour activist in Panyu, in the southern province of Guangdong.

The region's bustling ports and factories have made a huge contribution to China's transformation into the world's second-largest economy.

But as the country's growth slows and factories shut at an alarming rate, they have become ground zero for an explosion in strikes and worker protests.

According to data from Hong Kong-based rights group China Labour Bulletin (CLB), there were 2,774 across the country in 2015 -- more than the previous four years put together -- with unpaid wages the most common grievance.

As China's manufacturing hub, Guangdong has been hard-hit by the country's growth slowdown and had almost twice as many strikes and protests last year as any other province.

Unions represent one of the government's greatest fears: that economic dissatisfaction, a widening crack in one of the key pillars of the ruling Communist Party's claim to legitimacy, might lead to an organised political movement.

"Labour unrest is one of the things that keeps the Communist Party up at night," said Eli Friedman, an expert on labour relations at Cornell University in the US.

Beijing, he said, has closely studied how Poland's Solidarity union movement contributed to the fall of its communist government.

Authorities have spent hundreds of billions of dollars trying to prevent a similar scenario, by propping up failing companies to avoid mass unemployment.

They also tightly control tools such as social media to stop people organising effectively and have cracked down on groups that threaten to gather in large numbers, whether in front of a factory or in Tiananmen Square.

- 'Conflict of interest' -

The accusations against Zhu also come as Beijing wages a widening campaign against civil society, including the mass detentions of human rights lawyers.

Zhu, her husband said, only wanted to help employees protect their rights. But in early December, authorities detained her and two other members of the Panyu Workers Service Centre, along with at least four other activists.

Chinese state media vilified them, with the official Communist Party mouthpiece the People's Daily saying they had "plotted behind the scenes to organise and control labour strikes" that "seriously disturbed social order" and "trampled on workers' rights and interests".

Their work, it said, targeted the government, using funds provided by foreign organisations, including CLB.

But a factory employee who worked with Zhu and requested anonymity said that she "taught us how to not break the law, taught us legal knowledge".

"She gave so much, but society has repaid her with this kind of slander," the worker added.

The tactics have not stopped demonstrations: more than 60 strikes were reported nationwide in the first week of January alone.

Independent groups such as Zhu's actually help to resolve strike actions, according to CLB campaigner Geoffrey Crothall, by negotiating with angry workers and encouraging them to focus on "reasonable" demands.

"It's completely the opposite from what the government is pretending is happening," he said.

The state-run All-China Federation of Trade Unions is the country's only approved union and the only group legally allowed to collectively bargain on workers' behalf.

But many employees feel that it has not "adequately represented" them, Friedman told AFP.

"It's a typical practice to have the HR manager also serve as the union chair, which creates an obvious sort of conflict of interest," he said.

- Sobbing child -

Clothes and toys lie scattered around Wu's apartment. For over a month, he has balanced being the single parent of two children with fighting for his wife's freedom.

They met at Hitachi Metals, where she was his supervisor. She fought the company for workers' right to establish a union, a decision that cost her her job and started her on the path to activism.

Since her detention, Wu has seen her only a few times, and when he brought their daughter to the detention centre to nurse, he said, she barely recognised her own mother.

On one visit, a government official handed him a letter in her handwriting.

"Don't worry," it said. "You don't need to request a lawyer. Once I clearly explain the situation, they can't make difficulties for us."

Wu disbelieves its content "200 percent," he said, adding that police have also pressured him to not seek legal aid.

Police in Panyu declined to comment when asked by AFP.

Wu has hired a lawyer, but police have denied him access, he said. Now, he is left waiting.

"My wife helped a lot of people," Wu said, rocking his sobbing infant to sleep. "Including me."

dly/slb/cah

Hitachi Metals