This is being reported by Reuters, noting that the PBOC will scrutinise bulk dollar purchases by domestic firms, citing three sources with direct knowledge of the matter. Companies will need to seek approval for purchase of dollars amounting to $50 million or more, although there is no official announcement being made yet it would seem.
I'm guessing this is to try and smooth out the timing of these transactions and I would think it would not be best for the PBOC to peruse and restrict such purchases all too much. I reckon they would just want to manage the flows accordingly and then they can use that to decide how they want to step into the FX market to limit the depreciation in the Chinese yuan.
