GetUp has been accused of providing false and misleading information to a parliamentary inquiry into the 2016 federal election, which the activist group refutes.
Over a year-and-a-half, the inquiry sought information from the group about answers provided to its 2016 election vision survey, which asked people to rank the issues GetUp should focus campaigns on.
"Five times GetUp failed or refused to provide the full results of this survey. Instead providing misleading, and on one occasion, false information while giving implausible reasons for this refusal," Liberal MP Ben Morton told the lower house on Thursday.
GetUp lied about the top three issues its members wanted it to focus on and only gave the parliamentary committee correct information after the threat of summons, Mr Morton said.
The group listed "stopping the government handling over billions of dollars every year to big polluters" in its top three issues, yet the survey results did not reflect this.
GetUp members had instead ranked "dismantling Australia's cruel offshore detention regime" in their top priorities, but the group did not focus its election campaign on the issue.
"This was a serious, calculated and persistent 'cover-up'," Mr Morton said.
However, GetUp says it doesn't just use information provided in the survey to develop its election campaigns.
The group told the parliamentary committee in July that other membership surveys, voter polls as well as phone and online consultations are also used.
"Mr Morton should apologise for wasting everyone's time," a GetUp spokeswoman told AAP on Thursday.
"Back in July we called on Mr Morton to provide a written public apology. Today he has shown that he'd prefer to keep throwing grenades than correct the record."
The issue is expected to be raised in the House of Representatives next week.
