Trilogues have been studied as sites of secluded inter-institutional decision making that gather the Council of the European Union, the European Parliament (EP) and the European Commission. Trilogues, however, are not exempt from formal and informal party-political dynamics that affect intra- and inter-institutional contestation. The increase in Eurosceptics in the 2014 EP elections offers an opportunity to investigate their efforts to shape the position and behaviour of the EP negotiating team in trilogues. Therefore, this article investigates to what extent Eurosceptic party groups participate in trilogue negotiations and how mainstream groups deal with their presence. The analysis shows that the opportunities to participate in trilogues and shape the EP’s position are higher for those perceived as soft Eurosceptic MEPs, while mainstream groups apply a ‘cordon sanitaire’ to those perceived as being part of hard Eurosceptic groups – which reduces the chances of MEPs from those groups being willing to participate in parliamentary work.