Sinn Féin is refusing to endorse a human rights report due to be published by the Policing Board today.
Alex Maskey, one of Sinn Fein's members on the board, said a number of the report's 45 recommendations cannot be supported by his party.
He says republicans will not endorse the continued use of plastic bullets in any circumstances, while human rights training for all new officers is still not sufficiently rigorous.
Mr Maskey said: "The Policing Board has the direct responsibility to ensure that the PSNI complies with the highest standards of human rights in all areas of its work.
"While there has been considerable progress in recent years we are not satisfied that the Policing Board has been rigorous enough in its role of scrutiny and holding the police to account.
"Sinn Féin does not support or endorse a number of the recommendations in this report.
"Sinn Féin will not under any circumstances, endorse the use of plastic bullets, particularly against children.
"We are very disappointed therefore that the Policing Board has again supported the use of plastic bullets."
The DUP is accusing Sinn Fein of taking this stand for purely political reasons.