A draft news release detailing tax measures to be contained in an upcoming ways and means motion was mistakenly posted on the department's website for a few minutes late Thursday afternoon.
That forced Finance Minister Joe Oliver to hastily table the motion on Friday, earlier than planned, in order to give all Canadians full access to the information.
In a statement, Oliver called the incident "an administrative error" that was quickly rectified.
"Action was taken to take (the release) down within 10 minutes. I take this situation very seriously and have instructed the department to review its procedures to ensure it does not happen again."
NDP finance critic Nathan Cullen wrote Oliver on Friday about the leak of "potentially sensitive tax information."
"The leak and availability of this information, prior to it being made public, gave those with this information an opportunity for personal financial gain," Cullen said in his letter.
"This could obviously lead to insider trading and market distortions."
However, Oliver played down the sensitivity of the measures in the ways and means motion, saying most are aimed at implementing tax changes announced in last February's federal budget.
"There were no details of the fall economic update contained in the release," he stressed.
"These matters were technical changes with the vast majority having already been consulted on."
The motion does contain almost a dozen income and sales tax measures that were not included in the budget, including doubling the children's fitness tax credit to $1,000 — as announced by Prime Minister Stephen Harper on Thursday.