There are fears that thousands of jobs could be at risk at Tata Steel.
The Indian firm employs around 4,000 people at its Port Talbot site and is one of Wales' most important employers.
Reports over the weekend suggested it plans to shut two blast furnaces and replace them with electric arc furnaces, which could lead to thousands of job losses in the UK, including at the factory in Port Talbot.
The steel workers' union, GMB, said it is holding "urgent talks" with the company.
Ross Murdoch, GMB National Officer, said: "We spoke to Tata Steel senior management over the weekend to discuss these reports. The company will be arranging a meeting of the UK Steel Committee as soon as possible.
"At this meeting GMB and sister steel unions will be seeking a response and clarification from the company.
"Through our regular meetings with the Department for Business, Energy & Industrial Strategy, GMB has become aware some steel companies have sought Government support as they navigate their way through the Covid-19 pandemic."
In April, there were reports that Tata was seeking a loan from the UK and Welsh governments in the region of £500m after global orders slumped because of coronavirus.
In 2019, the company made losses of more than £370 million.
Another steel workers' union, Community, said: "Rest assured the unions will not accept the end of blast furnace steel production at Port Talbot, which would leave the UK unable to make a range of specialist steels.
"Steel production accounts for half the jobs at Port Talbot and this plan would devastate the town and the community. If necessary we will be prepared to fight to protect our members' livelihoods and the future of our industry.”
Analysis by ITV Cymru Wales' Work and Economy correspondent, Carole Green
"Firstly no decisions have been made and any strategic changes on the ground about how steel is made at Port Talbot are likely to come in years not months.
"We know Tata has asked for 500 million pounds to help with the impact of coronavirus on the business as demand has slumped from key markets like the car industry, which constitutes a third of the business at Port Talbot.
"The UK Government will be looking very closely at how sound the business was before lockdown and whether there is a robust plan to sustain it into the future.
"Changes could come in the form of making so-called 'Green Steel' from scrap metal rather than in a blast furnace, which has always been regarded as the gold standard for quality. We could see a hybrid approach, when an expensive investment on refurbishing a blast furnace is next needed. This is when the switch to an arc furnace could come running alongside one blast not two.
"The worry now about switching to arc furnaces would be that it needs fewer people, however it could retain steel making in the town and in Wales, albeit in a different form. From a community perspective it would avoid the shock and awe of a complete shutdown or quick pull out."
"Stephen Kinnock MP said it would be a "devastating blow" for the steelworks and the community if the blast furnaces were to be shut in Port Talbot.
The Labour MP for Aberavon said: "The steel workers in Port Talbot make the best steel that money can buy but they are trying to compete with one hand tied behind their back.
"It is very disappointing that this potentially game-changing plan has been submitted to the government without a conversation with the workers and Trade Unions."
The Welsh Government said it is aware Tata Steel is "exploring a series of decarbonisation options".
In a statement, the Welsh Government said it is continuing to work with Tata Steel in its planning for the long term. It said is meets with the company regularly and will be in discussions again shortly.
The statement continues: "We are committed to doing all we can to support a strong future for the industry, and remain committed to working with all governments in the UK to help achieve this. The Economy Minister regularly raises the subject of Tata and the steel sector with the UK Government."
Tata Steel has confirmed it is having "active discussions" with the UK Government about several options for the future of its UK operations.
A Tata Steel Europe spokesperson said: "Given prevailing market conditions and disruption caused by the COVID-19 pandemic, it is clear that our UK operations face structural challenges that need to be urgently addressed.
“At this stage no decisions have been made. It would therefore be inappropriate to comment on unsubstantiated speculation about the outcome of these discussions or the potential impact of any changes to secure our sustainable long-term future."