Voluntary organisations have until 18 November to tell the National Audit Office about their experiences of the Compact.
The spending watchdog is investigating the implementation of the public-voluntary sector partnership across central government.
Nick Hurd, the Minister for Civil Society, announced the study last year as part of a series of measures that he said would provide an "unprecedented level of scrutiny of the Compact".
The NAO was initially due to publish its findings in July but they are now expected by the end of the year.
According to the NAO website, the study will focus "on issues of accountability and transparency" and identify and highlight variations in practice. Its final report will make recommendations for improvements to the Office for Civil Society and other Whitehall departments.
Interested parties can write to: email@example.com.