The nuns, from the Hertfordshire-based order of the Daughters of Jesus, are angry that Mr Brown awarded himself a large pay rise at a time the company was planning to sack employees and reduce the pay of others. (Mr Brown now earns £475,000.)
The Daughters of Jesus, who own shares in other listed companies, plan to write to British Gas to seek an explanation of Mr Brown's actions.
They are also considering turning up at the annual meeting in May to challenge him in person. The meeting promises to be a traumatic affair for Mr Brown, with numerous shareholders planning to raise the issue of boardroom pay.
Sister Elizabeth Fox, the order's bursar, said: "I don't see how anyone is worth or needs £475,000. I don't see how anyone can accept such a pay rise when others in the company are seeing their salaries cut. I don't think this is a particularly religiousview. I would imagine it is a view shared by a lot of other people," she said.
Sister Fox explained the Daughters of Jesus did not have large shareholdings in any one listed company, but they did have a professionally-managed portfolio of investments.
"We are concerned to see that our investments are ethical. There is a certain injustice in Mr Brown's pay award. Many other religious orders have voiced their concern to me, and they too could also be attending the AGM."
The order has asked its financial adviser, accountants McIntyre Hudson, to contact other active shareholder groups to see if there is any action planned, and if so, can they join them.
Contact has already been made with UK Shareholders' Association, which is circulating a resolution proposing a change to the company's articles, which, if carried, would force the company to put future increases in directors' pay to a vote of shareholders.
A spokesman for the Catholic church said: "It is perfectly possible to read Catholic teachings about justice to employees and interpret Cedric Brown's pay rise unfavourably in that light.
"It is a matter of interpretation rather than overt policy, but that doesn't make such a view any less valid," the spokesman said.Reuse content