NSW Community Services Minister Pru Goward has to hand over all emails, phone records and minutes of meetings relating to a report revealing staff shortages in child protection.
It follows a call for papers passed by the NSW Legislative Council on Thursday morning.
"This will help get to the bottom of minister Goward's continued lies over the real number of caseworkers," said Opposition Leader John Robertson.
All year the minister has consistently claimed the state has more than 2000 case workers on the books.
But the the Ernst & Young Report found only 1797 of 2068 budgeted caseworker positions had been filled.
Ms Goward denied any knowledge of the report when it surfaced at budget estimates last week and again during question time.
But on Tuesday she admitted the draft report had been sent to her office multiple times and was on the agenda at a meeting in July.
"The minister has already been caught out misleading the NSW parliament," Mr Robertson said on Thursday.
The O'Farrell government will now be forced to provide documentary evidence about Ms Goward's knowledge of the report as well as advice provided to the minister about the report.
Premier Barry O'Farrell says he stands by Ms Goward.
"I support the minister, I support the statement she made in parliament," he told reporters.
Mr O'Farrell said Ms Goward had in March written to the former director-general of her department to ensure funds were being used to employ as many case workers as possible.
He added that the report wasn't "specifically discussed" during the meeting at which it was tabled.
The opposition wants an inquiry into "ministerial propriety"' which will investigate whether Ms Goward misled parliament, Fairfax Media reports.
Mr O'Farrell said he would be happy to cooperate and appear before any review.