The Hart-Scott-Rodino Act (HSR), the US merger control system, is based in the compulsory notification of transactions reaching certain thresholds.

These thresholds might seem low, especially when compared to those under European Commission Regulation 4064/1989, but relatively recent changes have removed a blanket exemption for acquisitions of foreign assets by foreign persons allowing a sale of non-US assets between two non-US parties to be covered by HSR.