The Government cut VAT by 2.5 per cent to 15 per cent for 13 months in November 2008, in an effort to spur trade. Some retailers held the same prices and kept the difference.
Conservative MP Peter Luff said: "Reintroducing VAT at the time of the January sales is thoughtless."
BHS, Sainsbury's, Marks & Spencer and other retailers have called the reintroduction an "administrative nightmare".
Shoots Garden Centres director Piers Mummery said: "It will cut into the margin we've enjoyed this year."
But HTA business development director Tim Briercliffe said the VAT increase was likely to go ahead, adding: "If VAT goes up and retailers are not prepared to put it up then they will lose out.
"It's going to be a mixture of those who will swallow the difference because they think products will be too expensive if they put them up, and others who will do it. We're not finding evidence that consumers are finding things too expensive. Retailers should try to increase prices accordingly."