The letters warn victims' advocates Helen Last and Judy Courtin that if there is ''any publication'' by them to a journalist or anyone that defames Ms Sharkey ''our client will not hesitate to take legal action against you without further notice''.
The letters were sent on November 2, but Ms Last - a consultant for the Melbourne Victims Collective - only received it on Thursday due to various circumstances.
Ms Last, who gave evidence to the inquiry last Monday, said the letter from Wisewould Mahony partner Robert McGirr misrepresented her and intimidated her.
Ms Courtin said she found it ''very threatening, intimidating and bullying''.
Ms Sharkey co-ordinates pastoral care, such as counselling, for people whom the Catholic Church accepts - through its Melbourne Response independent commissioner - suffered abuse.
She and The Age recently settled a defamation case concerning an article about complaints against her by abuse victims, as part of which The Age apologised and accepted that Ms Sharkey had not engaged in gross professional misconduct.
The Catholic Church in Melbourne, which has promised to co-operate with the inquiry, said through a spokesman that it had not sent and did not know of any such letters.
''Decisions about the publication of the testimony of Ms Last are for the parliamentary committee, and we acknowledge that parliamentary privilege protects the publication of all evidence accepted by and published by the parliamentary committee,'' he said.
Mr McGirr said on Sunday the letter had nothing to do with the inquiry. It ''was sent in response to The Age article, nothing more'', and warned Ms Last and Ms Courtin that if they said anything defamatory about Ms Sharkey she would sue.
Ms Last has written to Ms Crozier about the letter, asking her to confirm that the collective's submission, titled ''United in Truth'', would now be covered by parliamentary privilege.
''We have given permission for it to be published on the government website, however, in the light of this legal letter threatening defamation, I will need to know what risk we are facing through its publishing online.''
She told Fairfax Media on Sunday that she was conflicted because she had told the inquiry, without naming Ms Sharkey, that the collective believed Carelink lacked proper boundaries and had a conflict of interest.
Ms Courtin is a lawyer who helped Ballarat survivors of abuse frame their submission to the inquiry and has made another submission about her own PhD research into justice for victims under the various avenues open to them.
She is investigating whether abuse victims obtain justice through the three avenues open to them of civil court action, criminal court action, or the church's two protocols, Towards Healing and the Melbourne Response.
''Not only are they not finding justice, but their experience with the two protocols often retraumatises them,'' Ms Courtin said.