"I have sent a letter to the PCB appealing against the three million rupees ($35,000) fine imposed on me by the inquiry committee for my ball-tampering offense in Australia," Afridi told Reuters.
The all-rounder's decision to appeal came just two days after the board appointed him captain for next month's Twenty20 World Cup in the Caribbean.
Afridi was found guilty of ball tampering in the final one-dayer in Perth in February.
"When I have already served a two-match ban (from the International Cricket Council) for the ball-tampering incident then on what basis is the board punishing me for the same mistake again?” said Afridi.
Younus's lawyer Ahmed Qayyum said he had sent a letter asking the PCB to provide evidence of his client's offense.
"The charge sheet sent to my client does not specify any incident on the basis of which they handed such a harsh punishment," Qayyum said, referring to the indefinite ban Younus received earlier this month.
"We have asked the board to provide us evidence on the basis of which the inquiry committee decided Younus must be banned."
The PCB handed out the same suspension to Younus and former skipper Muhammad Yousuf after media reports of in-fighting between the pair during the unsuccessful tour of Australia.
Shoaib Malik and Rana Naved, who were banned for 12 months and fined two million rupees each, have also announced they will be challenging their PCB punishments.
