It was once an unruly force to be reckoned with, blocking toll roads and urging masses to walk off jobs, causing crippling industrial standstills.
But in the past months, the labour movement seems a shadow of its former self due to a split between the two largest labour confederations over which presidential candidate to support.
Mr Said Iqbal, who leads some six million labourers under KSPI, supports former general Prabowo Subianto, while Mr Andi Gani Nena Wea, who leads a similar number of labourers under KSPSI, says Jakarta Governor Joko Widodo is the man to back.
"The labour camp is split and it has been a divisive campaign, but these labourers need to understand that the new government will not be able to fulfil all election promises because it really depends on the quality of its new ministers," former state enterprises minister Sofyan Djalil told The Straits Times.
The two camps have called for their members to pledge support along their organisations' lines and have organised mass demonstrations of support. Though their members have been seen in uniform openly supporting their preferred candidates, it remains unclear if this translates into votes.
A survey by Poltracking Institute released on Sunday showed labourers were almost evenly split - with 44.9 per cent backing Mr Prabowo and 44.1 per cent backing Mr Joko, and the remaining undecided.
Rivalry between the two camps has intensified, raising concerns among businessmen of mass demonstrations or violence by supporters of the losing candidate after the presidential election on July 9.
There are also fears that the incoming president could cave in to pressures to implement populist measures to appease labour unions. Last Friday, some 100 members of KSPI arrived in Jakarta after a four-day "long march" route of nearly 300km from Bandung, West Java, in a show of solidarity for Mr Prabowo.
On the other side of the ring, Mr Andi Gani's KSPSI members have donned matching T-shirts bearing Mr Joko's face and engaged in social work across provinces in Jakarta to promote their presidential pick.