The EU transparency register for the European Parliament and the European Commission was launched in the summer of 2011 to better expose outside influence on EU law and decision-making.

With around 6,000 organisations signed up as of November 2013, the register, which is not mandatory, allows people to search an online database and see details on how much a company is spending on lobbying.

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A company does not have to be based in the EU capital to register. Of the 6,000 or so entities in the register, only around 2,800 are said to be in Brussels.

But critics say much of the data supplied by the entrants is either incorrect or out-of-date, and that many influential companies, NGOs and law firms have yet to sign up.

Of the around 1,100 quality checks performed since March 2012, around 780 contained an error of some sort. Most were later corrected.

The commission estimates that between 60 to 75 percent of Brussels’ lobby corps can be found in the online database.

Many organisations don’t have to bother with the database.

Churches and religious communities, political parties, and local, regional and municipal authorities are exempted from the register although those who represent them in Brussels are expected to sign up.

EU member state governments, third country governments, international intergovernmental organisations as well as their diplomatic missions are not expected to register either.

Law firms exempted

Law firms, unless they engage in “interest representation”, are also exempted.

Some law firms not in the register are criticised by transparency groups because they lobby or have cosy relationships with senior officials in Brussels.

Michel Petite, a corporate lawyer with big tobacco clients at law firm Clifford Chance, was a member of the European Commission’s ad-hoc ethics committee until he stepped down last December.

Clifford Chance Brussels’ branch office has a team of over fifty lawyers that deal with regulatory and anti-trust issues. They are not registered.

Another outstanding issue is requiring law firms in the database to publish their client lists.

The idea has met resistance from within the European Parliament.

Parliament vice-president German centre-right Rainer Wieland, who heads transparency issues in the assembly, says publishing the lists would conflict with some member states’ client-attorney confidentiality rules.

Other big companies like Amazon, which hire out consultancies to do their work, are not in the register either. Yet the reach of the US giant among EU lawmakers has proven extensive.

Last year, numerous data protection regulation amendments made by some MEPs were simply copy-pasted from Amazon.

The company recently posted a job ad for a Brussels-based public policy senior manager. Among the tasks demanded in the job description is “to shape EU political and legislative developments”.

Getting companies like Amazon to sign up has divided those supporting the register into opposing camps.

Mandatory - or not?

The European Commission says it expects the register to become “quasi mandatory” or at least very difficult to avoid.

The European Parliament, for its part, wants it to be mandatory.

Opponents of the mandatory register argue it is better to create incentives to attract more entrants.

Some incentives are already in place.

Only those registered are allowed access to the European Parliament buildings. But others, like requiring outside experts who advise the European Commission to register, have yet to take hold.

Opponents also argue it is too complex to impose a mandatory register because there is no legal basis. Either a Treaty change or a unanimous decision among member states is needed to make it mandatory.

MEPs in the constitutional affairs committee want the European Commission to issue a proposal to make it obligatory by 2016.

Asked if the commission is prepared to put forward a proposal, a commission spokesperson said it is too early to tell.

"We have to see the final resolution as adopted by the EP plenary before any formal reaction is possible," noted the spokesperson.