PFA chief Gordon Taylor has warned Di Canio that he cannot be a "law unto himself" after members of Sunderland's squad raised a complaint with their union following a series of club fines.
Di Canio has fined a number of his players after a club night out hit the back page headlines prior to their final game of the season at Tottenham.
The Italian was unapologetic in his public condemnation of some of his players - but now they have brought the PFA in.
And PFA chief Taylor is far from happy with Di Canio.
"He cannot be a law unto himself," Taylor told the Daily Mirror.
"We're aware of player unrest at some comments made publicly, and other situations. A number of players are involved.
"We're aware of Paolo Di Canio's comments - it's something we had to deal with [when the Italian was manager] at Swindon as well.
"Our rules for discipline are agreed with the Premier League and Football Association."