Citing more than seven pages of redactions that were sent in response to requests for an eight-page document, Barton added that "it is unclear why Yahoo feels such an acute need to hide its actions from the public." The companies in question have tried mightily to inform the public about what the non-exclusive deal would and would not do, officials have said. Executives have testified on Capitol Hill and discussed the issue at a number of public events. The firms also launched YahooGoogleFacts.com to provide more clarity. DOJ is expected to issue a statement on the deal soon.

Update: Yahoo issued a statement saying that the firm has "cooperated fully" with Barton's staff and will continue to do so. For months, Yahoo has been working with DOJ, members of Congress and others reviewing the proposal. Google and Yahoo have also delayed the ad program's launch to provide regulators with more time and information, officials noted.