It said it is "deeply concerned about the lack of progress so far on the issue of over-representation," referring to advisory groups where business lobbyists outnumber NGOs and civil society groups.

The transparency group says that the only way to avoid "privileged access for certain specific interests" is to establish consistent membership criteria and called in the letters for an "open and transparent process" for the selection of such expert groups.

It also asks commission president Jose Manuel Barroso what he intends to do about those groups where it is already clear that there is an over-representation of business interests.

According to the group, EU industry commissioner Guenter Verheugen is responsible for 127 expert groups but only 19 of these include membership details. As an example, it points to the expert group on biotechnology which has 20 industry representatives, six academics and no NGOs.

Meanwhile, his research colleague Janez Potocnik oversees 97 groups of which just 17 have their details listed while energy commissioner Andris Piebalgs is in charge of 36 groups of which three contain membership details.

For health commissioner Androulla Vassilou, the tally is 70 closed groups to eight public groups while environment commissioner Stavros Dimas is said to preside over 95 closed groups and only three open ones.

The letter to Mr Dimas says that the so-called supervisory group of the voluntary commitments of car manufacturers to reduce CO2 emissions is carrying out consultation for the commission "but is only consulting the views of business," whereas as CO2 emissions "affect the whole of society."

The commission promised earlier this year that the process of collecting and publishing the names of members of the different groups shall be completed by the summer. It also pointed out that experts from national governments and agencies made up two-thirds of those in the panels.

Running behind schedule

According to Alter-EU, the total number of expert groups has increased by more than 40% since 2000, with one group for every eight officials working in the European Commission. Total membership of the groups runs to over 50,000.

A commission spokesperson admitted the process is a "bit slower" than they thought because of data privacy issues surrounding making all the names public but the intention is to make all names public eventually.

"They are busy updating just as it comes. It is not going to be a big bang step," said the spokesperson.

The rise in the number of lobbyists, think tanks and NGOS in Brussels as well as the increasing tendency of Europe to set the regulatory agenda around the world has made the influence of these groups a highly political issue.

In June, the commission officially launched its public online lobbyist register, but the move was immediately criticised by civil society groups for lacking teeth because it is a voluntary system.