The Tudeh Party sharply criticized the launching of ESKI, denouncing it as a 'yellow union'. In state companies, workers were obliged to join ESKI in order to keep their jobs. In other sectors, coercion and bribes were used to pressure workers to join ESKI. The strength of ESKI was concentrated in railway plants, munition factories and the tobacco industry. However, ESKI had limited success. There was a distinct gap between official membership figures and the number of genuine followers. ESKI leaders were generally not experienced labour organizers. In the analysis of the U.S. labour attache, William J. Handley, ESKI was in the hands of government functionaries who, in Handley's view, were 'socially illiterate'. On November 12, 1946, Tudeh mobilized a 24-hour general strike to condemn the murder of a railway worker. Tudeh accused ESKI of having hired thugs to carry out the assassination.
When the Tudeh-led CUC was suppressed in May 1947, ESKI hoped to be able to fill the void, but such a breakthrough never occurred. ESKI was also caught up in the political intrigues between Ahmad Qavam's Democratic Party of Iran on the one hand and the royal court and army on the other. Sharif-Emami was removed as head of ESKI, and replaced by Khosrow Hedayat.
On August 30, 1947, ESKI, EMKA and another small union signed an agreement to coordinate their activities. CUC had refused to join the cooperation. However, the deal only lasted for two weeks, after which ESKI and EMKA excluded the third grouping. On October 28, 1947, ESKI and EMKA organized a labour congress in Teheran. Present were 84 ESKI delegates and 46 EMKA delegates. The cooperation between ESKI and EMKA did not last, however. And in December 1947, shortly after the break between the two centers, ESKI thugs carried out an attack on an EMKA club building. The attack on EMKA further discredited ESKI.
Latter period
As of December 1947, ESKI claimed a membership of 75,000. At the first congress of ESKI, held in November 1949, 21 out of 36 delegates were engineers. Only two delegates were workers. At the labour congress held in February 1951, a new trade union centre called the Iranian Trade Union Congress was formed. Both ESKI and EMKA merged into the ITUC. ITUC inherited ESKI's ICFTU membership.
