Liberal Leader James Cowan wants the Senate rules committee to investigate whether "outside interference" with the independent audit into Senator Mike Duffy's expenses could constitute a breach of privilege.

In the formal letter of notice submitted earlier today, Cowan argued that the alleged interference "began virtually from inception," starting with a call purportedly made by Prime Minister Stephen Harper's then-chief of staff Nigel Wright to "a member of the [Senate internal economy] committee" seeking changes to the press release announcing the referrals to Deloitte.

Using the latest batch of court filings to bolster his claim, Cowan argued that the alleged interference "began virtually from inception," starting with a call purportedly made by Prime Minister Stephen Harper's then-chief of staff Nigel Wright to "a member of the [internal economy] committee" seeking changes to the press release announcing the referrals to Deloitte.

Senate Liberal Leader James Cowan (Fred Chartrand/Canadian Press) In the court documents, RCMP Cpl. Greg Horton alleges Wright and Duffy committed bribery, fraud and breach of trust when Wright wrote Duffy a cheque for more than $90,000 to cover Duffy's questionable Senate expenses.

Horton also alleges the Prime Minister's Office tried to interfere with an audit into Duffy's expenses, as well as with the Senate committee's report on the audit.

According to Cowan, that initial communication from Wright was only the beginning.

"The interference continued when Mr. Michael Runia, a managing partner with Deloitte, telephoned auditor Gary Timm allegedly at the request of the Prime Minister's Office, seeking information about the [Duffy] audit," he noted in his submission.

"That this call ... was inappropriate," Cowan told his colleagues during his address to the Senate chamber this afternoon, has been acknowledged by everyone."

What remains unknown, in his view, however, is why the call was made at all.

Cowan also brought up those now infamous emails between Wright and other PMO staffers on the audit process.

"Why should the chief of staff to the PM be sending emails discussing the desired outcome of an independent audit?"

If the Speaker were to find a prima facie breach of privilege, Cowan said he would propose that the matter be sent to the Senate rules committee for further investigation.

Not surprisingly, Conservative Senate Leader Claude Carignan appeared unmoved by Cowan's concern that the privilege of the upper house may have been violated.

How, he wondered, would a simple request for a change in the wording of a press release constitute interference?

"That's unbelievable," he told his colleagues. "I'm awestruck."

Independent Senator Anne Cools also spoke out against Cowan, arguing that his proposed remedy would effectively be asking one committee to rule on the work conducted by another.

After hearing interventions from both sides, Senate Speaker Noel Kinsella took the matter under advisement, and will likely hand down his ruling next week.

Cowan's move came the day after the Conservative-controlled Upper House nixed a motion that would have ordered the Senate internal economy committee to question Runia about his involvement in the Duffy audit. He made a similarly unsuccessful bid to hear from Runia after the committee met with the Deloitte audit team last week.

Read the full notice letter below. Mobile users, click here to view in your browser.