More than 400 Canadian academics have demanded a halt to a government audit of a think tank, critical of the government, saying Prime Minister Stephen Harper’s administration is trying to intimidate and silence dissidents.

The appeal was made by 421 academics in an open letter addressed to Revenue Minister Kerry-Lynne Findlay, released on Sunday.The group of academics said authorities seem to have targeted educational charity Canadian Center for Policy Alternative (CCPA) because it frequently criticizes the administration’s agenda. “The decision to audit the CCPA is politically motivated to intimidate and silence its criticisms of your (Findlay’s) government policies,” said the group.

The academics called for a moratorium on all audits of the think tanks until the revenue ministry imposes a neutral and fair selection process. “Instead of trying to muzzle and impede sound and legitimate research, it is now time for you to try to promote more effectively the public good in the form of sound critical research for which Canadian researchers are respected internationally,” said the group.

The revenue agency began an audit of CCPA last October, claiming its research and education material posted on the charity’s website appeared “biased” and “one-sided.”

However, the group of academics argued that the think tank conducts its research in a “fair and unbiased way,” and that its frequent criticism of Harper’s government policies does not make the charity a partisan organization. The educational charity is among the 52 organizations that are being audited by the agency under a CAD 13.4-million program launched in 2012 to determine if any charities are engaged in forbidden partisan activities. Initial audits targeted environmental groups, which have been critical of the conservative government’s energy and pipeline policies; however, the agency later widened its target area to poverty, international aid and human-rights groups, who are criticize the government’s policies.

The audit program has been dubbed “advocacy chill” as some groups self-censor its findings to avoid the possibility of being audited.