However, in 1950, following the advent of the global Cold War, and taking advantage of the sense of crisis precipitated by the sudden outbreak of the Korean War, conservative Japanese government and business leaders launched, with the tacit approval of US Occupation authorities, a "Red Purge" to remove communists and suspected communists from government and private-sector jobs.
[1] On May 1, 1952, Sōhyō spearheaded a nationwide day of protest against the perceived one-sided nature of the Peace Treaty ending the Occupation of Japan.
Although most of these activities were peaceful, a violent clash between protesters and police outside the Imperial Palace in Tokyo led to several deaths and injuries and became remembered as "Bloody May Day.
Sōhyō's period of militancy culminated in 1960 when it took a leading role in the massive Anpo protests against revision of the US Japan Security Treaty, as well as the large-scale strike at the Miike Coal Mine in northern Kyushu.
However, both these efforts ended in disastrous defeats, and thereafter Sōhyō increasingly retreated from contentious strikes in favor of more moderate workplace actions.