Opposition politicians accused officials in the Prime Minister's Office of threatening the integrity of the independent Commissioner of Lobbying, in the wake of revelations that the watchdog was investigating a lobbyist firm with close connections to senior Ottawa Conservatives.

The Globe and Mai, citing an unnamed government official, reported that the lobbying commissioner was investigating Navigator Ltd. — whose chairman is a former colleague of Guy Giorno, Prime Minister Stephen Harper's chief of staff — but did not say why. The chairman, Jamie Watt, did not return calls requesting comment.

By law, investigations by the lobbying commissioner are to remain secret.

Liberal MP Paul Szabo said leaking the fact that the firm is under investigation could taint that investigation.

"The prime minister has undermined the confidentiality required by the Lobbying Act, and compromised a potential investigation," Szabo said in the House of Commons on Tuesday .. [Read the rest of the story]