Workers at a Chinese factory owned by Foxconn, Apple Inc's main manufacturer, threatened to jump off the roof of a building in a protest over wages just a month after the two firms announced a landmark agreement on improving working conditions.

The protest happened in the central city of Wuhan at one of Foxconn's plants. The company employ some 1.2 million workers in China assembling iPhones and iPads, among other products.

It involved some 200 workers, the Hong-Kong based activist group Information Centre for Human Rights said.

A spokesman for Hon Hai Precision Industry, the listed unit of the Foxconn group, said the protest concerned workplace adjustments and involved workers new to the plant. He said it was not a strike.

"The dispute has already been settled after some negotiations involving the human resources and legal departments as well as the local government," the Taipei-based spokesman, Simon Tsing, said.

Foxconn, China's largest private-sector employer, and Apple agreed to tackle violations of working conditions and improve working environments.

The deal was agreed almost two years after a series of worker suicides at Foxconn plants focused attention on conditions at Chinese factories and sparked criticism Apple's products were built on the backs of mistreated Chinese workers.

On Tuesday, Apple reported that its fiscal second-quarter net income almost doubled after a jump in iPhone sales, blowing past financial market expectations.

Tsing declined to say how many employees were involved in the latest dispute. He said no-one had actually jumped off any building.

The Information Centre for Human Rights said one of the complaints of the workers was that they earned less in Wuhan than they had in their previous jobs. They returned to work after police intervened, it said.

Global protests against Apple swelled after reports spread in 2010 of a string of suicides at Foxconn's plants in southern China. Apple agreed to an investigation by the independent Fair Labor Association to stem criticism that its products were built in sweatshop-like conditions.

Although Apple and Foxconn agreed to lift workers' salaries, wages have been rising quickly. The 159 million migrant workforce saw an average salary increase in 2011 of 21.2 percent, the National Bureau of Statistics said