The executive is thought to be ready to approve proposals designed to curb the practice of former Commissioners moving to lucrative jobs in the private sector soon after they leave office.
The problem has been highlighted most recently by the appointment of former Commission president José Manuel Barroso at Goldman Sachs.
The Commission is now set to propose an extension of the so-called "cooling-off" period - the time that elapses between an official leaving office and taking up a post in the private sector.
It is believed the idea is that the cooling off period should be extended from 18 months to two years for ex-Commissioners and from 18 months to three years for former Presidents.
Reform of ethics rules for ex-Commissioners will be discussed on Wednesday at the weekly college meeting.
However, transparency campaigners say they are dissatisfied with the proposal, saying it does not go far enough.
An open letter to Commission President Jean-Claude Juncker has been sent by the Alliance for Lobbying Transparency and Ethics Regulation (ALTER-EU).
ALTER-EU is a coalition of over 200 public interest groups and trade unions concerned with the increasing influence exerted by corporate lobbyists on the political agenda in Europe.
Juncker recently told Belgian newspaper Le Soir he would propose to reform the code of conduct for Commissioners.
At Wednesday's meeting, he is expected to present his proposal to his fellow Commissioners.
But the ALTER-EU open letter says, "What has so far transpired from his plans, however, seems very weak - an extension of the cooling-off period to just two years for ex-Commissioners and three years for former Presidents will fail to prevent future ethics scandals of the sort caused by Barroso, Kroes, de Gucht and others."
ALTER-EU is now urging Juncker to put forward an "ambitious proposal that shows strong political leadership for a strengthened code of conduct, outlining which measures will be crucial for a true reform of commission ethics."
Corporate Europe Observatory researcher and campaigner Margarida Silva said: "It is an important step forward that the Commission now acknowledges and addresses the role that weak rules have played in creating its systemic ethics problems.
"But the proposals put forward so far lack ambition and are not enough to prevent future ethics scandals."
ALTER-EU says it has made several attempts to start a dialogue with the Commission to discuss its recommendations.
"Disappointingly, the Commission has so far refused to enter into a dialogue on the issue with any parts of civil society, including ALTER-EU," said a spokesperson.