From Wikipedia:
Consecration of bishops without papal approval had been condemned by Pope Pius XII in his encyclical Ad Apostolorum principis, which described the sacramental activity of bishops who had been consecrated without such approval as “gravely illicit, that is, criminal and sacrilegious”.[25] The Roman authorities were unhappy with Lefebvre’s plan, but they began discussions with him and the SSPX which led to the signing on 5 May 1988, of a skeleton agreement between Lefebvre and Cardinal Joseph Ratzinger, the prefect of the Congregation for the Doctrine of the Faith and the future Pope Benedict XVI.
On Pope John Paul II’s instructions, Cardinal Ratzinger replied to Lefebvre on 30 May, insisting on observance of the agreement of 5 May and adding that, if Lefebvre carried out unauthorized consecrations on 30 June, the promised authorization for the ordination to the episcopacy would not be granted.
On 3 June, Lefebvre wrote from Écône, stating that he intended to proceed. On 9 June, the Pope replied with a personal letter, appealing to him not to proceed with a design that “would be seen as nothing other than a schismatic act, the theological and canonical consequences of which are known to you”. Lefebvre did not reply and the letter was made public on 16 June. For the first time the Holy See stated publicly that Lefebvre was in danger of being excommunicated.
On 30 June 1988, Archbishop Lefebvre proceeded to ordain to the episcopate four priests of the SSPX. Monsignor Antônio de Castro Mayer, the retired Bishop of Campos dos Goytacazes, Brazil, assisted in the ceremony. Those consecrated as Bishops were: Bernard Fellay, Bernard Tissier de Mallerais, Alfonso de Galarreta, and Richard Williamson.