At the time, a number of organisations had called for the government to delay the planned January 2016 start date.
The former partner did not tell Google the information was confidential, the source said.
Reuters could not establish if Google was a client of PwC Australia at the time, and if it used the information in any way.
What sources told Reuters matches information in the letter, which was publicly released with the name of the company that received the confidential information redacted.
Tax officials told parliament in May they foiled several attempts by unnamed multinational firms to subvert the multinational anti-avoidance law in early 2016, months after confidential information had leaked.
Persons:
PwC, Peter Collins, Collins, Tom Seymour, Lewis Jackson, Emelia Sithole, Sonali Paul
Organizations:
Google, Reuters, PwC Australia, PwC, Tax, Board, Thomson
Locations:
Australia, SYDNEY, PwC Australia