Former Defence Secretary Liam Fox in 2010 threatened to sue a Labour MP over comments she made about his trips to Sri Lanka, Sky News reports.
Dr Fox's complaints arose from a campaign email Siobhain McDonagh sent to members of the Tamil community in her constituency ahead of the 2010 General Election.
The email contrasted Foreign Secretary David Miliband's visit to Sri Lanka, in which he challenged the government on their human rights record, with a number of visits made by Dr Fox, funded by the Sri Lankan Government and a mysterious organisation called the Sri Lanka Development Trust.
McDonagh has told Sky News her researcher received an "angry" call from Dr Fox in which he shouted down the phone threatening legal action.
"He was certainly deeply sensitive about this. For all we know there were things in that email which were more significant than we thought," she said.
"Perhaps he was concerned we knew more than we did."
No legal action was formally taken by Dr Fox and the issue was not raised again.