According to the letter published in The News, the PCB chief claimed that CAS had no legal or moral right to approach the PCB.
''It seems to us to be direly plain that the CAS lacks jurisdiction to entertain any appeal and WADA lacked the standing to launch one. Therefore we do not understand how you can entertain such an application still less make peremptory orders providing for compliance within short time scales over the holiday period,'' the letter read.
''We would not abide by any orders made by any CAS panel as we do not wish to take any step which might be seen as having accepted that CAS has jurisdiction,'' Mr Ashraf said.
Earlier, PCB received a letter from CAS' David Caslerly who had sought all the relevant material and dates suited to the board for the start of hearing the case in CAS.
After testing positive for nandrolone, Shoaib was banned for two years while Asif was slapped a one-year ban before a PCB appeal panel lifted the punishment.
The PCB has always maintained that WADA or the CAS has no jurisdiction to hear such an appeal and pointed out that the board is not a signatory of WADA code and thus does not abide by its rules.
The board yesterday named Asif in the Pakistan team for the tour of South Africa while Shoaib was left out ostensible for lack of fitness.