To answer that we have to go back to a Fair Work Commission (FWC) ruling of April 30 last year.

In 2012 the workers negotiated a new enterprise agreement, which expired in 2015 - but the conditions in the deal continued to apply.

In late 2017 the coal terminal management asked the FWC to scrap the agreement - which is legal once it has passed its expiry date.

According to FWC's senior deputy president Jonathan Hamberger's ruling the 2012 agreement was "negotiated in a strong economic environment" where a record 14.7 million tonnes of coal passed through the terminal.

The future looked rosy for the terminal - but things went sour.

"As it turned out, however, market conditions significantly deteriorated in 2012," Commissioner Hamberger wrote.

"Coal prices fell significantly and PKCT customers significantly cut their output."

READ MORE: Coal terminal workers to strike after lockout

The commissioner noted some of the "generous" conditions of the 2012 agreement, including employer superannuation payments of as much as 20.5 per cent and the "Team" system that saw workers rather than management decide workload priorities.

Negotiations for a new agreement began in March 2015 and continued for two years, with both sides coming up with proposed deals only for the other side to reject them.

According to the commissioner, the workers' rejection of a 2017 offer lead to a "hardening" of the coal terminal's position and the move to scrap the 2012 deal.

However, he acknowledged the union representatives seemed more flexible than the workers.

"I consider that while the employee representatives had genuinely accepted the need for major change, including the dismantling of the 'team' system, this was not necessarily the case for many of the employees," the commissioner wrote.

READ MORE: Workers locked out for another week

He agreed with the terminal's application, saying the 2012 deal "needs to go".

"I am not confident that the bulk of the workforce (as opposed to their representatives) have fully accepted this fact," Commissioner Hamberger wrote.

In negotiating a new deal, he also felt both side had "at times taken positions that made it more difficult to reach agreement".

With that in mind, he gave them a year to sort it out - ruling the agreement would be terminated on March 29, 2019.

With that deadline now fast approaching and no new agreement still in place, there has been a number of strikes by workers and lockouts by management (the latter of which is legal when in response to industrial action by workers).

While the two parties are close on a number of issues, the key sticking point is an employment security clause.

The union wants the 2012 clause to remain in place, which would prohibit the company from sacking a worker and replacing them with contract labour.

The terminal's latest version of this clause states it would “investigate available avenues to avoid forced redundancies” including reducing the number of contractors – but only if the employee and contractor are doing the same work".

The unions say this falls short of a guarantee and claim the terminal wants to get rid of the workers and replace them with cheaper contractors.

The coal terminal claims that's not its intention.

Unionists have suggested the company plans to keep locking out workers out until the March 29 deadline is reached, at which point the basic award would kick in and their pay and conditions would drop drastically.

That would appear unlikely given a lockout is only legal if it follows actual industrial action by employees, not threatened action.

The next date to watch is February 27, which is when workers are due to return after the latest lockout finishes.