Amid the chaos on Sydney trains this weekend, commuters are questioning why the strikes are happening in the first place.

The Rail, Tram and Bus Union (RTBU) confirmed industrial action is going ahead from Friday morning to Sunday mid-morning, with Sydney and inter-city services halted across the network.

NSW Transport secretary Josh Murray said operators around the network are "scrambling" to organise replacement transport services.

He urged commuters to "prepare now" for delays, road congestion and service shutdowns. 

It's all happening due to a breakdown in negotiations between the RTBU and the NSW government.

Why is the union striking on Sydney trains?

The union has made a series of demands as part of their current enterprise bargaining with Sydney Trains and NSW Trains.

So far, negotiations have not been successful and the union instructed its members to not operate the network.

What are the union's demands?

The RTBU, which represents a cross section of workers in different roles from maintenance managers, CCTV operators, train drivers, technicians, cleaners and station staff, asked for a series of changes to pay and work conditions. 

The latest log of claims showed approximately 245 items are up for negotiation.

A 32 per cent pay rise over four years or an 8 per cent annual increase has been called for.

When it comes to super, the union wants an additional 1 per cent employer superannuation contribution, and for super to be payable on all hours worked and while on parental leave or workers compensation.

Training allowances have been requested, as well as meal allowances for call outs. 

Where wages and allowances — including penalty rates — are not paid correctly or on time, the RTBU wants a penalty to be paid to the employee by the employer.

A 35-hour work week without a reduction in weekly renumeration is also on the cards.

Flexible work is another core focus. The union said provisions must not be unreasonably refused.

Where an application is refused, they said there must be a written explanation provided and an appeal process managed and administered by the employing agency. This includes decisions on hybrid working and mandated days in office. 

Workers should have all overtime paid as double time, the claim said. Overtime should be paid on the day too.

The final major demand is centred on leave.

The RTBU wants annual leave increased to five weeks for non-shift workers and six weeks for shift workers. 

They said long service leave needs to be available after seven years, and five years for pro rata on retirement.

Plus, employees undergoing fertility treatment need to be entitled to one day of paid leave for each occasion of appointments associated with fertility treatment.

RTBU NSW branch secretary Toby Warnes accused the state government and Sydney Trains of not negotiating in good faith.

"Our action was designed not to use commuters as a ping pong ball," he said.

"We hope that the premier intervenes [in negotiations] and we see some sense."

NSW government's response to union demands

In response to the demands, the state government in June offered rail workers 11 per cent over three years. 

The union has rejected this counter offer.

Transport Minister Jo Haylen said more than 50 bargaining meetings have taken place so far, including 28 meetings with more than 90 union delegates.

The NSW government is expected to meet with the union again on Wednesday afternoon to continue negotiations.

"We've been very clear that [the RTBU demands] are not affordable," she said on Wednesday.

"That is not something we are able to deliver, which is why we're in ongoing negotiations — not only about wages, but a range of other pay and condition issues.

"I hope to resolve this agreement as quickly as possible."