At least two Sutherland Shire councillors have sought legal advice and made complaints to police about the letter, titled No More Developers in Liberal Party Branches, which made a number of defamatory accusations.

The letter called for councillors Kent Johns, Kelly Knowles, Melanie Gibbons and Kevin Schreiber to be expelled from the Liberal Party and blamed them for the party's loss of control of the council.

It reached mailboxes on Thursday and appeared to have been selectively sent to delegates listed in the Cook Federal Electoral Conference.

Several Liberal Party members who received the letter are understood to have contacted the office of Cook MP Scott Morrison to inquire and complain about the letter, although there has been no suggestion Mr Morrison or his office were involved in any way.

The letter was a matter of concern to senior Liberals because party branch member lists, containing personal details including addresses, are only available to a select few within the organisation which should make a large-scale mail-out impossible.

Party sources said the membership list used to source the addresses of recipients for the letter appeared to be relatively old, meaning the information could have leaked out some time ago and made tracking the author through the lists impossible.

Cr Johns said he was aware of the letter and its contents and had received many calls of support in response.

"The reaction has been nothing but massive support from the people I know ringing me up and giving me copies of it,'' he said.

"People are disgusted this is going on.''

Cr Schreiber said he received a similar response.

"I've had many phone calls from people who are irate about receiving such garbage anonymously,'' he said.

"I just find it outrageous.''

Crs Knowles and Gibbons also expressed disappointment about the letter.