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Apple is among 30 technology companies targeted by Durbin, who serves as the majority whip of the U.S. Senate on Capitol Hill. Others named by the senator include Facebook and Skype.
Durbin's inquiry follows Google's decision to not comply with censorship laws imposed by the Chinese government.
"Google sets a strong example in standing up to the Chinese government's continued failure to respect the fundamental human rights of free expression and privacy," Durbin said in a statement obtained by Reuters. "I look forward to learning more about whether other American companies are willing to follow Google's lead."
Last month, Apple's presence in China made the news when workers at one of Apple's overseas manufacturing partners in Suzhou, China, went on strike to protest what Wintek employees felt were unsafe working conditions and unfair wages. Workers of the plant destroyed and vandalized some equipment, and 300 riot police were dispatched to the location.
The Wintek dispute was quickly resolved with bonuses paid to employees, and the work stoppage reportedly had no effect on the plant's production. The Wintek factory is a component supplier for Apple's iPhone.
Last year, Apple released its 2009 responsibility progress report, which found that more than half of Apple's partners' factories in China were not properly paying their workers. In addition, 23 of 83 surveyed factories were not even paying some of their employers China's minimum wage.
In 2006, Apple voluntarily conducted its first audit. That survey found most facilities from manufacturer Foxconn to be in compliance.
On the sales side, Apple has made a serious of late push to establish its brand in China. Recently, the company revealed it has sold more than 200,000 iPhones through carrier China Mobile since it debuted late last year.
"We are very, very focused on the quality of the point of sale and consumer experience," Apple Chief Operating Officer Tim Cook said on the company's most recent earnings report conference call. "We would prefer to move slow because we are building the brand for the long-term and we are very much focused on the long-term in that market, because we think there is significant potential there."
The company also revealed that Mac sales in China increased nearly 100 percent year over year in the last financial quarter.