A new study by Transparency International (TI) shows MEPs from the far-right ENF group drew the most income from sources other than their elected post. UKIP's Nigel Farage was also on the list.
A report by anti-corruption NGO Transparency International published on Tuesday revealed that Euroskeptic members of the European Parliament receive the highest earnings from secondary jobs and private activities.
According to Transparency's report based on publicly available disclosures, nearly one third of the European Parliament's 751 members (MEPs) disclosed private income that surpassed their monthly €8,400 ($9,873) net salary and €4,000 allowances.
The practice of legislators having a second job has been dubbed "moonlighting" which TI says has the potential for negative consequences, as it can create conflicts of interest and prevent lawmakers from dedicating themselves fully to their elected duties.
Additionally, the anti-corruption NGO says, outside income can be used as a potential channel for members to trade insider information or legislative action for money, and serve as a conduit for illicit campaign financing.
The European United Left and Nordic Green Left (GUE/NGL) came in bottom of TI's list with 18 percent of its members making extra income.
TI says moonlighting is common in democratic countries. A common justification for secondary jobs is that elected officials can stay in touch with their profession and have a link to it when their public service is finished.
'Moonlighting' revenue grows with tenure
More than half of the 35 members of the far-right Europe of Nations and Freedom Group (ENF) declared secondary incomes.
The list includes Brexit campaigner Nigel Farage, who earned €30,000 per month in 2017 from activities outside the European parliament, a sum well above the €1,000 salary he held at the beginning of his mandate.
Jean-Luc Schaffhauser, of Marine Le Pen's party, was another politician who saw his wealth grow during his time as an MEP. Schaffhauser disclosed a nine-fold increase in personal revenue since his election.
But there are also left-wing MEP's who came in with a large income. Italian center-left legislator Renato Soru tops the list of earnings by individuals with €1.5 million derived from his telecom business.
Belgium, France, Italy, Germany on the list
The TI report also ranked moonlighting by country.
Germany has 96 MEPs, of whom 40 percent have earned a combined total of €1.4 million in outside activities since 2014.
The country with the highest percentage of moonlighting MEPs was Belgium, with 62 percent of lawmakers earning a combined €1.2 million.
French MEPs came in as highest earners, with 51 percent of them earning over €4 million in secondary revenue since 2014.
Italy only had 18 percent of its EU lawmakers declare secondary income, but they earned €2.6 million.
At the bottom of the list was Estonia. One MEP declared earnings of €17.
jcg/jm (Reuters, dpa)