In December 1976, the PSOE celebrated its 27th Congress in Madrid, and began to disassociate itself from the demands of the PCE, affirming that it would participate in the next call for elections for the Constituent Cortes. At the beginning of 1977, the year of the elections, Suárez decided to confront the problem of legalizing the PCE. After the public indignation aroused by the Massacre of Atocha in January 1977 against trade unionists and Communists, Suárez decided to talk with PCE secretary-general Santiago Carrillo in February. Carrillo's willingness to cooperate without prior demands and his offer of a "social pact" for the period after the elections pushed Suárez to take the riskiest step of the transition: the legalization of the PCE in April 1977. However, throughout this critical period the government began a strategy of providing greater institutional space to the (UGT) Socialist union, in comparison to the then Communist-oriented CCOO. The manner in which a unified trade union was strategically countered is an important feature of the Spanish transition, as it limited radical opposition and created the basis for a fractured industrial relations system.