ChainCatcher news reports that, according to market sources, the U.S. Customs and Border Protection (CBP) is detaining certain imported Bitmain Antminer mining machines at U.S. entry points. The equipment involved includes Bitmain's Antminer S21 and T21 series, which are the latest ASIC mining machine series from Bitmain.Sources indicate that the FCC and CBP have not targeted other ASIC manufacturers such as MicroBT or Canaan. Aside from revealing that the FCC has requested a freeze, U.S. Customs and Border Protection has not provided specific reasons for taking this action to the affected parties, nor has it indicated how long the goods will be detained.