The article analyzes different types of coalition formations that were established and hoped to be established during the transnationally coordinated campaign against the second Czech nuclear power plant in Temelín. The case study concentrates on the role the EU played in the campaign. Due to the ongoing accession process, the opponents of the power plant viewed this process as a unique opportunity for halting the plant’s construction. They actively lobbied the European Commission to make the Czech Republic’s accession to the EU conditional on discontinuing the construction. The perceived significance of the EU explains the political strategies the opponents developed at the end of the 1990s, in order to persuade the European Commission to become involved in the campaign.