Boris Johnson has urged the government to back European Parliament calls for improved lorry safety, in an effort to cut the number of cyclist deaths.
The London mayor said he was "deeply concerned" that ministers had rejected moves to enlarge windscreens and windows to prevent driver blind spots.
This could save "hundreds" of lives across Europe, he said.
The government said it shared Mr Johnson's concerns but his plan would not bring "practical changes".
Of the 16 cyclist deaths in London in 2011, nine involved heavy goods vehicles, of which seven were construction lorries, according to the mayor's office.
Mr Johnson's cycling commissioner, Andrew Gilligan, is in Brussels - with representatives from 130 other European cities, including Madrid, Amsterdam and Copenhagen - to lobby Euro MPs and the European Commission to amend the current EU directive on lorry design.
The campaigners say cabs should have larger windows and windscreens to make it easier to spot approaching cyclists.
They also advocate making cab fronts "safer", so they do less damage when lorries hit bikes or pedestrians.
The amendments will be debated in the European Parliament on 11 February, with the London mayor's advisers saying the vote looks "finely balanced".
If passed, the plans will then be considered by the Council of Ministers, representing EU member state governments.
Mr Johnson, said: "This is a once-in-a-decade opportunity for the EU to remove some of the blockages which prevent us from making lorries safer in our cities.
"If these amendments, supported by dozens of cities across Europe, can succeed, we can save literally hundreds of lives across the EU in years to come. I am deeply concerned at the position of the British government and urge them to embrace this vital issue."
Last year, the government said: "Any mandatory requirement for cabs to have a new profile should be supported by an impact assessment. As far as we are aware, there is no impact assessment to support such a change."
Responding to Mr Johnson's demands, a Department for Transport spokesman said: "We share the mayor's concerns about the potential benefits of improved cab design and we want to see changes in the industry.
"Where we are not supporting European Parliament proposals, it is simply because they will not produce practical changes in cab design and could lead to additional bureaucracy for Britain."
He also said: "It is vital we do all that we can to protect cyclists from HGVs, which is why we launched the HGV Task Force with Transport for London to target dangerous drivers, vehicles and operators.
"We are reviewing exemptions to current HGV safety regulations and are pressing the European Commission to introduce urgent changes to requirements for mirrors on HGVs."
The government was spending £278m on cycling during this parliament, including £35m on safer junctions, the spokesman added.