MPs are set to vote on whether to grant the Government control of British Steel.
Both the Commons and the Lords for a highly unusual Saturday sitting to debate a Bill.
The emergency legislation is aimed at blocking the company's Chinese owners, Jingye, from .
The plans would see taxpayer money used to provide materials to the steelworks and open the door to a transfer of ownership.
Sir warned the future of the firm “hangs in the balance”.
Ministers hope to secure a private partner to open up co-investment options for a transition.
But urgent temporary action was seen as necessary to keep the plant running until longer-term plans are agreed.
The Commons sitting started at 11am and the House of Lords from midday in the first parliamentary recall on a Saturday since 1982, when MPs returned after the start of the .
Other significant recalls during recent years included a midweek sitting during the summer recess in August 2021 to debate the evacuation from Afghanistan.
In a letter to MPs, Commons Speaker Sir said he was satisfied the “public interest” requires the recall to debate the Steel Industry (Special Measures) Bill.
Jingye, which bought British Steel in 2020, has said it invested more than £1.2billion to maintain operations amid ongoing production instability and “significant” financial losses of around £700,000 a day.
The Government says the new law would allow it to order raw materials for Scunthorpe's blast furnaces amid fears supplies are on the brink of running out.
Ministers would be able to direct the company's board and workforce, and ensure anyone at the plant “who takes steps to keep it running, against the orders of the Chinese ownership” can be reinstated if they are sacked.
The proposals to close Scunthorpe's furnaces had sparked fears of job losses at the plant, which employs thousands of people.
Business Secretary said Jingye had confirmed the plans despite months of talks and a £500million co-investment offer from Government.
He said this left ministers “no choice” but to act to spare job losses and save the plant.
Unions welcomed the move but Tory leader accused Labour of having “bungled the negotiations” and said “their incompetence has led to a last-minute recall of .”
Liberal Democrat Sir called the debate an opportunity to advance “a serious plan for the sustainable future of domestic steel production”.
leader reiterated his backing for nationalisation.
