Under parliamentary rules those deputies not returning to Parliament receive a transitional allowance equivalent to one month per year in which their mandate has been exercised.
They need to have been an MEP for at least for one year to be eligible.
The Commission adopted the register four years ago but Council and Parliament are yet to do so.
Under the rules, lobbyists cannot meet high-level Commission decision-makers without having first joined the transparency register.
While the “not on the register, no meeting” principle applies to EU Commissioners, it still does not apply to MEPs or the Council.
Transparency International (TI) has estimated that more than 50 percent of ex-Commissioners and 30 percent of ex-MEPs who have left politics are now working for organisations on the EU lobby register.
A TI report published earlier this year said that companies “are employing former officials to gain access, influence and proximity to policymaking.”
“We ask for a mandatory cooling-off period as we believe that an MEP going to work for lobbying organisations on the EU transparency register straight away raises some ethical issues and leaves the Parliament open to undue influence” Transparency International spokesman
It added, “For example, 50 percent of Google’s registered lobbyists used to work for the EU. 26 MEPs who left the European Parliament in 2014 are currently working for Brussels lobbying consultancies.”
A TI spokesman said, “We ask for a mandatory cooling-off period as we believe that an MEP going to work for lobbying organisations on the EU transparency register straight away raises some ethical issues and leaves the Parliament open to undue influence, conflicts of interest and in some cases regulatory capture by special interest groups.”
There are currently no rules in place regulating post-mandate activities for MEPs. For EU Commissioners, there is an 18-month cooling-off period.
The demand is part of a broader election campaign mounted by the group which also targets candidates in the elections and the Commission presidency, who are urged to sign a pledge committing themselves to “be transparent and ethical in all their parliamentary activity.”
This, TI says, involves publishing details on the use of their MEP allowances and accepting meetings only with registered lobbyists and publishing the details online.
Candidates are also asked to agree to a ‘cooling-off’ period after leaving the Parliament.
The TI spokesman said this means that they would not lobby for an organisation on the EU Transparency Register while still receiving the transitional allowance.
If elected in the 23-26 May poll, candidates are also asked to support the creation of an independent body for ethics oversight that monitors conflicts of interest, the “revolving door” and lobby transparency.
TI says a “strong ethics oversight body”, like those in France and Canada, could oversee ethics and revolving door cases in the Commission, Parliament and Council and be able to impose sanctions.
The group, and others, have raised concern about the ‘revolving door’ phenomenon in EU institutions in the wake of ex-Commission President Jose Manuel Barroso’s move to Goldman Sachs last year.
The spokesman said, “Corruption remains one of the main barriers to realising the original vision of a Union. Perhaps most importantly, it also fuels the growing inequality that is one of the biggest barriers that divide the people of Europe today."
Elsewhere, party leaders in the UK have been challenged to back greater openness and transparency in this month’s European elections campaign.
The Open Knowledge Foundation has written to UK Prime Minister Theresa May, Labour leader Jeremy Corbyn, Scottish First Minister Nicola Sturgeon and other party leaders across the UK to outline five key demands.
Chief executive Catherine Stihler, a former MEP for nearly 20 years, said it is “vital that the UK returns MEPs who will champion a fairer and more open society.”