The General USP Chapters <232> and <233> describe the specification of limits for metallic impurities in pharmaceutical preparations and their analytical determination. The publication of these two chapters was originally planned for the 1st December 2012. A coalition of companies from the pharmaceutical industry, trading firms and industrial associations (IPEC America, IPEC Europe, GPhA, CHPA, SOCMA-BPTF and further ones) has recently issued a formal appeal to the USP to postpone the official publication of these chapters. The coalition thinks that if the USP acted separately, it would lead to the impossibility to find a textual conciliation with the requirements laid down in the ICH Guideline Q3D. In the end, this would mean that different requirements would be applicable to medicines on the American market and on the European one. In turn, this would cause delays in the authorisation of medicines and potential drug shortages. An article published in the Pharmaceutical Technology from 2 November 2012 defines precisely the coalition's position.
So far, the Guideline ICH Q3D entitled "Impurities: Guideline for Metal Impurities" has been existing as Step 1 document and is going to soon reach Step 2. Yet, the final Step 4 status of the guideline won't be reached before the end of 2013. For that reason, the USP has announced in an official revision bulletin its decision to implement both chapters on 1st May 2014.
Please find further information in the PharmTech article "An Industry Perspective on Harmonization and Implementation of ICH and USP Requirements".
In comparison, you can have a look at the Guideline ICH Q3D (Step 1) here and the USP chapters <232> and <233>.