TAIPEI — Labor rights groups are stepping up their campaign against a Taiwanese supplier for Apple Computer.

They have accused the company, flat-panel maker Wintek, of exploiting workers at its factories in Taiwan and its subsidiary's factory in China.

The groups organized a protest outside Apple's Taipei office on Thursday morning, targeting the U.S. computer giant for the first time.

They say Wintek has not fully addressed their demands after months of negotiations, so they're taking their campaign to one of its high-profile customers.

"We want to go through Apple to put pressure on Wintek," said Chu Wei-li, 30, secretary-general of the Taipei-based National Federation of Independent Trade Unions, a key organizer of the protest.

The labor groups allege that Wintek fired more than 600 workers without warning in December, slashed salaries and made employees work unpaid overtime to fill rush orders.

The rights groups further allege that a Wintek subsidiary in Dongguan, China, cut workers' salaries without negotiation, has unacceptable working conditions and illegally fired 19 workers after a strike in mid-April. (See detailed allegations here.)

Wintek denies any wrongdoing. In an e-mail, spokesperson Susie Lee said Wintek posted record net losses in 2008 due to the global downturn, and was forced to institute "cost-saving measures."

It says it gave laid-off workers compensation packages, and that all of its policies are in line with local laws and regulations, as well as its supplier "code of conduct" agreements.

"We hope ... certain persons or groups do not [make] unfounded allegations to harm Wintek's reputation and affect the normal business activities of a law-abiding company," Lee wrote. "Wintek shall take relevant necessary steps including legal action in order to protect company and stakeholders interests."

Apple's Asia spokesperson Jill Tan said in an e-mail, "Apple is committed to ensuring the highest standards of social responsibility wherever our products are [made]," and pointed me to the firm's corporate responsibility information.

Apple conducts regular audits of suppliers to make sure they comply with Apple's code of conduct, Tan said, and "we require corrective actions when we find violations."

It's not the first time Apple has come under scrutiny for labor conditions at its Asian suppliers. In 2006, Apple did an inspection of one supplier — a subsidiary of a different Taiwanese firm — after a media report alleging poor working conditions at one of its factories in China.

Apple found "excessive" work hours by laborers making its popular iPod player at the plant, according to the BBC. It said the supplier corrected the violations and would from then on enforce a "normal" 60-hour work week.

The current labor action is unusual in that it's being taken on behalf of both Taiwanese and Chinese workers. It's supported by labor groups in Hong Kong, mainland China, Japan and South Korea, according to a press release about Thursday's protest.

On Thursday morning, about 30 protesters from local labor rights groups and trade unions held signs and chanted slogans, including "black-heart business" (heixin qiye), in front of Apple's Taipei office.

One protester held up an Apple laptop with the Chinese characters for "responsibility" on the screen. Behind, some 25 police officers stood by.

Some 15 laid-off Wintek workers joined the protesters later. Many wore surgical masks to prevent being identified, because they still hope to be re-hired at the firm's central Taiwan factory.

"If the company finds out you came here to protest at Apple, they will put you on a blacklist," explained Liu Wan-ling, of the Taiwan Labor Information and Education Association.

One 37-year-old laid-off worker came to the protest with his 3-year-old son in tow. He said he was fired last December without warning or explanation, after working for the firm for nine years.

When he showed up for work, his boss told him, "You don't need to come here, you're laid off — take all your things away."

"I'm here to ask for justice," the worker said. "My family needs income, so we can eat."

The protesters and former Wintek employees want Apple enforce its own supplier "code of conduct" and force Wintek to improve working conditions at its factories and rehire laid-off workers.

Chu says if their demands aren't met, they plan to continue protests at Wintek's next shareholders' meeting in June.

The workers and labor groups say Wintek should rehire now that its sales have recovered.

Apple's net profits for its fiscal quarter ending March 28 rose 15 percent over the same period a year ago.

Wintek's sales plummeted in the last quarter of 2008, according to information on its website.

But since January its sales have steadily recovered, with month-on-month increases of 26 percent, 15 percent and 13 percent in February, March and April.

Wintek was also at the center of rumors in March that Apple might make a netbook or similar product, with touch-screen panels supplied by the Taiwan contractor.

Wintek did not respond to a request for details on what it currently produces for Apple, and Apple said it does not comment on "supplier relationships."

More on labor unrest:

Is the 'boss-napping' story overblown?

Turkey's May Day protests turn fierce

Intel is at home in Costa Rica — for now