Trade union Unite has asked Will Hutton, head of the new public sector pay inquiry, to investigate "glaring pay differentials" in the voluntary sector.
Hutton, who is executive vice-chair of the Work Foundation, has been appointed to lead a fair pay review into public sector pay by Prime Minister David Cameron.
Cameron said the highest-paid employer in a public body should earn no more than 20 times as much as the lowest paid.
Unite, which has 60,000 voluntary sector members, wants state-funded charities that breach the 20:1 pay ratio to be included in the review.
Rachael Maskell, national officer for the not-for-profit sector at Unite, wrote to Hutton this week, saying: "We would very much want to highlight the problems experienced in the sector, especially in the light of this government's determination to make wider use of the sector for the delivery of public services."
A spokesman for Anchor said it was a "large and complex organisation" and "it is right that the pay of our chief executive reflects the scale of our organisation".