A widely-criticised tax on women's sanitary products is expected to go before Parliament today after MPs added their voice to a campaign for the charge to be scrapped.
Sanitary items, including disposable and reusable products, are currently subject to a reduced five per cent VAT rate - but protesters say this is still too much.
Ministers have said EU rules prevent them from reducing it below that figure, however campaigners hope that with a renegotiation of Britain's membership on cards, this could change.
Dozens of Labour MPs, led by shadow chancellor John McDonnell and joined by rebel Tories as well as Lib Dem and Ukip members, will try to amend the Budget to abolish VAT altogether for the items.
More than 250,000 people have now signed a Change.org petition calling for the change.
They argue that the items should not be classed as "non-essential luxury items", especially when books, newspapers, motorcycle helmets and various other items are rated at zero.
If it is voted in, Chancellor George Osborne would be forced to draw up a strategy within three months on how negotiations on scrapping the tax would proceed with the EU. A progress update would have to be provided by April.
Eurosceptics in the Tory party have lent their support to the cause too, hoping to use the case as an example of why sovereign states should regain control over taxation.
Harwich and North Essex MP Bernard Jenkin is one of 11 Tories to have put their name to the amendment - and said he believed many more would be prepared to vote on it as it was "hardly a choice for women that they have to buy sanitary products".
Ukip health spokeswoman Louise Bours labelled it a "tax on women", while the SNP's Alison Thewliss agreed, adding: "It is absurd that while men's razors, children's nappies and even products like Jaffa Cakes, exotic meats and edible cake decorations are free from VAT, women are still having to pay additional costs on what is already an expensive yet vital product.
"The failure of this Tory Government to negotiate the abolition of VAT on sanitary products over a period of five years suggests that either they are inept or they aren't genuinely committed to ending this unfair tax on women."
Labour cut the rate from the then-standard rate of 17.5 per cent to the lower rate of five per cent in 2000, but was prevented from going any lower by the European rules.
Any change would require a Commission proposal and the unanimous agreement of all 28 member states.
However, whether there is any appetite for such a move in some EU countries is uncertain.
The French parliament recently threw out a bid by socialist MPs to cut tax on sanitary products from 20 per cent to 5.5 per cent, with the Paris government arguing it would have cost it £40m in lost revenues.