The Social Labour Party (, PST) was a Brazilian political party. Founded in 1983, with the publication of its manifesto and statute, it received permanent registration in 1990 and, three years later, merged with the Renewal Labour Party (PTR), creating the Progressive Party. The party was recreated in 1994 and contested every election from then until 2003, the year in which it was merged into the Liberal Party.
According to one of its leaders, Dalmo Honaiser, the PST was a centre-right party based on the alliance between medium and small entrepreneurs, liberal professionals and workers. The party's manifesto included support for medium and small businesses, the strengthening of democratic institutions and the progressive taxation of unproductive land as a means of carrying out agrarian reform.
In January 1989, an application submitted by Honaiser was approved, and the PST was granted provisional registration. That same year, it participated in the coalition supporting the presidential candidate Fernando Collor de Mello, from the National Reconstruction Party, as did the Social Christian Party and the Renewal Labour Party (PTR). From May to June 1990, the PST organized its first national convention and obtained permanent registration from the TSE. Under his leadership, the party once again received congressmen from other parties. In October 1992, a parliamentary bloc was formed between the PST and the PTR — then chaired by the governor of the Federal District, Joaquim Roriz — which revealed the intention of merging the two parties. This merger was carried out in February 1993, giving rise to the Progressive Party.
However, the approval of a 5% electoral threshold that would be implemented in 2007, vetoed by the Supreme Federal Court in 2006, excluded most of the parties from access to free electoral advertising on radio and television and to public funding, among them the PST. For this reason, the party was merged into the Liberal Party in 2003, together with the Workers' General Party, in order to guarantee the right to these benefits.