A Commons committee has said official copies of Acts of Parliament should be printed on archive paper to save money.
But member David Amess, Southend West MP, told the BBC he had had "second thoughts" and vellum should remain.
Fellow member James Gray, MP for North Wiltshire, said switching to paper would save "very little money, if any".
He was late for the meeting in October when the Commons Administration Committee decided to back a call from Lord Laming that Acts of Parliament should be recorded on "high-quality archive paper" instead of the vellum.
It said specialised printing on vellum cost too much and top quality archive paper could last for 500 years.
Lord Laming said the "slightly over Â£100,000 per year" cost of vellum could not be justified, when archival paper was "superior for print quality". An online database of legislation is also kept.
The change must be agreed in the House of Commons, which rejected a previous bid to ditch vellum in 1999.
Now one committee member has changed his mind.
"I should have given more careful consideration to what we had been asked to decide upon. I now believe that I made a mistake in not voicing my concerns then," Mr Amess told BBC Sunday Politics West.
"It's very precious and is at the heart of the United Kingdom's tradition as being the mother of all parliaments."
Paul Wright, manager of vellum manufacturer William Cowley, said he was "gobsmacked" at the committee's decision. He calculated the average yearly cost at nearer Â£47,000.
North Wiltshire MP Mr Gray said vellum would last for 5,000 years at least and "can be kept in an ordinary cupboard" while paper would require "a new archive centre" with environmental controls to stop it degrading.
"I can't think why it is that this committee in Parliament are thinking about changing something that's done perfectly well for 1,000 years. It's a real piece of Parliamentary history," he said.

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Unseeded Puig, 22, beat the German world number two 6-4 4-6 6-1.
Reigning Australian Open champion Kerber, 28, simply could not match the intensity of her younger opponent in the deciding set.
Earlier, Petra Kvitova of Czech Republic beat USA's Madison Keys in three sets 7-5 2-6 6-2 to win bronze.
"It's just amazing," said Puig. "I know my country really appreciates this and I wanted to give it to them. The way that I did it tonight, I wouldn't want it any other way."
Puig, who was born in Puerto Rico but raised in Miami, added: "I always have been 100% loyal to where I was born and the roots I was raised in.
"I still have family in Puerto Rico and I have been back to visit quite a lot. I think it honestly is my favourite place to go when I want to go to the beach or see family.
"That island has given me so much. So much love and support throughout my career and I just wanted this one for them."
There will be a fifth Olympic medal for Venus Williams after the 36-year-old reached the mixed doubles final with Rajeev Ram.
Williams, the singles champion in Sydney in 2000 and winner of three doubles golds with sister Serena, made early exits from the singles and women's doubles.
But Williams and Ram defeated India's Rohan Bopanna and Sania Mirza in the mixed semi-finals, and will play fellow Americans Jack Sock and Bethanie Mattek-Sands for gold.
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An MP who backed moves to scrap Parliament's centuries-old tradition of printing laws on calf skin has admitted he "made a mistake".
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Monica Puig beat Angelique Kerber in three sets in the women's singles final to win Puerto Rico's first ever Olympic gold medal.