The letter was sent in response to accusations by the Sri Lankan high commissioner that Sitsabaiesan was trying to do just that by claiming she faced political intimidation while on a personal trip to the country.
Mulcair said the controversy was only created when Sitsabaiesan was followed, and that she "was right to be concerned."
Sitsabaiesan, who is of Tamil heritage, travelled to the South Asian country on Dec. 28, 2013 to visit relatives and learn about human rights. In a statement released earlier this month, the MP said she was warned by Sri Lankan officials during her private visit that she could be arrested and deported.
"I recently arrived in Sri Lanka to visit my extended family and visit the places that were once home for me, during the earlier stages of my life and the civil war in Sri Lanka; but [I] was subject to political intimidation," the statement read.
The commission took issue with the words "political intimidation," which High Commissioner Chitranganee Wagiswara called "grossly incorrect" in her letter to Mulcair dated Jan. 8.
"I also believe you would not want the MPs of your Party to make arrogant and patronizing statements about foreign states which creates a bad reflection on your Party and your policies," she wrote.
Mulcair had his own strong words in his response, saying that the SriLankan government's "human rights record continues to cause significant concern around the world."
He went on to urge the Sri Lankan government to hold an independent, impartial international inquiry into allegations of human rights violations and war crimes.
Followed after warning of possible arrest
According to fellow New Democrat MP Paul Dewar, Sitsabaiesan was followed and closely monitored by authorities from the moment she arrived for her visit.
Authorities showed up at Sitsabaiesan's hotel one night to try to meet with her but she did not respond, Dewar said.
He said officials were concerned that Sitsabaiesan had met with a Sri Lankan MP and had visited an orphanage. The visits involved family, he added, noting the local MP was a cousin.
Sitsabaiesan is not the first parliamentarian to stir up a bit of controversy while travelling in Sri Lanka.
Two Green Party MPs — one from Australia, the other from New Zealand — had their passports confiscated in November just before a planned news conference in Sri Lanka to describe human-rights abuses they were told of during their trip.