Nine of Britain's biggest brewing and pub companies are urging the prime minister to stop the Crown symbol on beer glasses being scrapped.
Brewers say the change is a "needless intrusion"
The Crown has been in use since 1699 as a guarantee of the size of pints and half pints.
But now it is set to disappear, replaced by a European Union-wide "CE" mark instead.
Campaigners say the change is another example of "excessive interference" by bureaucrats in Brussels.
The EU's Measuring Instruments Directive came into force last October and requires the UK to phase out the Crown in favour of the Conformite Europeenne logo.
But pubs and brewers say the Crown should be allowed to remain on glasses alongside the EU symbol and now they are asking for Tony Blair's help to save it.
In a letter to the prime minister, they say the new law is a "needless intrusion" into a system which has worked well for more than 300 years.
"We feel that it has been imposed on our industry without consultation and against the wishes of our consumers," they write.
"This directive is yet another in a long line of examples of excessive interference from Brussels which only serve to undermine support for the EU among business leaders and the wider public."
Among the signatories are JD Wetherspoon's chairman Tim Martin, Giles Thorley, chief executive of Punch Taverns, and Anthony Fuller, chairman of Fuller's brewery.
Trade minister Jim Fitzpatrick was asked about the Crown's demise in a Parliamentary written answer last week.
He did his best to appease opponents of the move, saying: "Pint glasses which were marked with the Crown stamp and placed on the market before that date remain lawful.
"There is therefore no requirement to remove existing Crown-stamped glasses from use."