"It is common knowledge the highest structure between congress, the annual national conference, ratified a decision taken by the national executive committee (NEC) in May to expel him," secretary general Narius Moloto said.
He said it was disrespectful of the Marikana organising committee to have allowed Mphahlele to speak, knowing that he was no longer a member of the party.
"The PAC will be writing to the committee to express its concern about its lack of sensitivity on such an important matter," said Moloto.
A commemorative rally was held on Friday to mark the first anniversary of the shooting at Lonmin's Marikana mine, near Rustenburg in the North West.
Thirty-four miners were killed on August 16 last year when police fired on them while trying to disperse and disarm them at Lonmin's operations in Marikana.
Another 10 people were killed in strike-related violence in the preceding week.
Last Friday 500 delegates at the PAC's two-day conference in Boksburg, on the East Rand, decided to uphold a decision to expel Mphahlele. – Sapa