"We are deeply concerned about recent developments in China," the two companies said in a joint statement sent to the Congressional Human Rights Caucus.
"We urge the US government to take a leadership role in this regard and have initiated a dialogue with relevant US officials to encourage such government-to-government engagement."
The two companies claim that they lack the power to address the issue of online censoring. Google, for instance, gave in to a demand by the Chinese government in January to block access to certain information.
Yahoo and Microsoft were both asked to appear at a briefing in Washington, but failed to show up, as did representatives from Cisco and Google.
Their decision sparked criticism from committee members who accused the
companies of turning a blind eye to the situation in China's for financial gain.
The Microsoft/Yahoo statement aimed to refute those claims.
"We do not consider the internet situation in China to be one of 'business as usual'," they said.
"Beyond commercial considerations, we believe that our services have promoted personal expression and enabled far wider access to independent sources of information for hundreds of millions of individuals in China and elsewhere in the world."
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