Tata Steel has said its current operations are financially unviable and it will focus on producing greener steel.
The company will build a £1.25bn electric arc furnace after the UK government contributed £500m towards its cost.
But it will end the production of steel from scratch, known as virgin steel, this year.
Mark Davies has worked in Port Talbot for 42 years, and wanted staff of all ages to be protected from redundancies.
“We want to see the next generations making a good living there,” he said.
“My boy is only 28, he’s in the cold mill. And it is a worry about where they’ll get jobs going forward.”
Mr Davies said he wanted to see Labour “come off the fence with a firm commitment” about reversing Tata Steel’s plans.
The unions would like to see at least one blast furnace to remain operational until the electric furnace has been built.
As well as its financial concerns, Tata Steel has said it would be a safety risk to begin construction while hot metal was still being produced on site.
“I think it’s important we go up and show a presence in parliament, for the government to see how serious we are,” Gary Keogh said.
A veteran of the steelworks, Mr Keogh said he “expects some answers from the government about why they’re prepared to throw our community and our industry away”.
Those travelling by train are members of Community, the union that represents most of the workers in the “heavy end” of Port Talbot’s steelworks.
An additional 300 jobs may go at Tata’s Llanwern site, in Newport, in three years’ time.
Jacqueline Thomas, who has worked there for nearly two decades, said the plant is like a “second family to me”.
“At the moment the second family is being destroyed, we’re under a tremendous amount of stress,” she said, speaking outside the UK Parliament.
“It’s predominantly a very young workforce, there’s young lads I know that have had children and got married, and I look upon them sometimes as my own children.
Speaking at a news conference in Cardiff, Welsh Labour Economy Minister Vaughan Gething said “hundreds of millions of pounds” more UK government money was needed to allow a “fairer transition for a sector that is good for growth and essential for our collective security”.
Prime Minister Rishi Sunak has stressed his government is committed to steelmaking, and provided Tata with £500m to avoid the whole Port Talbot plant closing with the loss of 8,000 jobs.
Mr Gething met junior UK government business minister Nus Ghani on Tuesday morning.
The meeting came after failed attempts by Mr Gething to meet Ms Ghani’s boss, UK Business Secretary Kemi Badenoch.
Mark Drakeford told the Welsh Parliament he was “genuinely baffled” that Rishi Sunak could not find the time to take a call from him about Tata on Friday.
In First Minister’s Questions, Mr Drakeford said former prime minister Theresa May had spoken to him when Ford announced the closure of its Bridgend engine plant in 2019.
Mr Drakeford made the request to Downing Street on Friday morning, Welsh Secretary David TC Davies was available instead.
‘Treated with contempt’
Also during the question session, Conservative Senedd leader Andrew RT Davies disagreed with the plans to close both blast furnaces in Port Talbot, saying that keeping one open was “a feasible objective for the transition to arc furnaces”.
His view differs from that taken by his Conservative colleagues in Westminster.
Earlier, a Plaid Cymru Senedd member said that her party would support any decision to take industrial action over closures at Tata.
Sioned Williams, the MS for South Wales West, said: “This is an existential crisis for them
“They’ve been treated with contempt to be frank. Not only from Tata but I also think from the UK government.
“Plaid Cymru will be standing by them,” she added.