The Congressional Budget Office yesterday doubled down on its report, Options for Taxing U.S. Multinational Corporations, in response to a January 24, 2013 letter from House Ways & Means Chair Dave Camp charging that the report was "heavily slanted and biased":

This letter responds to concerns you raised about the CBO's report, Options for Taxing U.S. Multinational Corporations, which was released on January 8, 2013. We continue to believe that it presents the key issues fairly and objectively and that its findings are well grounded in economic theory and are consistent with empirical studies in this area. Nevertheless, because of the complexity of the subject and the diverse views of experts in the field, we agree that it would have been desirable to seek comments from more outside reviewers. It is always our goal to seek outside reviewers for CBO studies who represent a broad range of views and perspectives.
Following is a discussion of the various issues you raised regarding the report.

• The Hill, CBO Defends Tax Report From GOP Criticism
  
• Reuters, Lawmaker, Budget Agency Spar Over Taxing Corporate Profits

This dispute is similar to last year's charge by Senate Republicans that the Congressional Research Service had released a biased report on the impact of tax rates on economic growth:

• CRS: An Economic Analysis of the Top Tax Rates Since 1945 (Sept. 17, 2012)
• Dems, GOP Trade Barbs After CRS Pulls Report on Tax Rates and Economic Growth (Nov. 2, 2012)
• Republican Staff Study: CRS Report on Tax Rates Is Flawed (Nov. 14, 2012)
• CRS Re-issues Report: Tax Rates on Rich Have 'Negligible' Effect on Economic Growth (Dec. 14, 2012)