A study by transparency group ALTER-EU says that "too many" law firms in Brussels are absent from the EU lobby transparency register "while clearly running EU lobbying services."
Many of the nine law firms highlighted originate in the United States where they are registered in the compulsory US lobby register, says the Alliance for Lobbying Transparency and Ethics Regulation.
"The boycott of the voluntary EU lobby register is further evidence to back our demand that European Commission President Jean-Claude Juncker should introduce a legally-binding register," says the Brussels-based group.
The analysis, 'Lobbying law firms - unfinished business', published on Tuesday (May 31), comes as the Commission's three month consultation on a mandatory transparency register comes to an end.
However, the Commission's proposal for a mandatory register would, claim ALTER-EU, be mandatory in name only and not backed by law.
"The Commission must acknowledge that there will always be some lobbyists who will seek to take advantage of voluntary lobby registration and not bother to sign up", says Nina Katzemich from LobbyControl, who authored the analysis for ALTER-EU.
"Our analysis shows nine cases of law firms, many of whom promote their EU lobby operations on their website, but who have not signed up. We believe that these nine are just the tip of the iceberg."
The nine examples, she says, also illustrate that law firms in Brussels can be "powerful lobbyists."
Because they understand the technical details of upcoming directives, on behalf of fee-paying clients, they can discuss them with officials or draft amendments for EU parliamentarians, says ALTER-EU.
"One law firm, for example, boasts about being a 'leader in helping companies, industry associations and governments navigate and shape EU rules' on its website.
"Several of the highlighted law firms actively support the Transatlantic Trade and Investment Partnership (TTIP), no doubt recognising the profit opportunities likely to come from the proposed, but controversial, investment arbitration system.
"In the US, lawmakers finally opted for a legally-binding lobby register because law firms continued to refuse to sign up under the voluntary model", Katzemich says.
"We are very sceptical that the Commission can tackle this problem in Brussels without a legally-binding system. A register which is mandatory in name only will simply not do the trick."
Meanwhile, European ombudsman, Emily O'Reilly, has opened a "strategic inquiry" into how the Commission carries out conflict of interest assessments for its approximately 40 special advisers, chosen to give Commissioners particular expert advice.
O'Reilly's inquiry follows complaints regarding the appointment of former German Christian Social Union (CSU) Chair Edmund Stoiber as head of the European Commission's high level group on administrative burdens.