Transport executives are beginning their legal action against the government to save a project to bring trams to Liverpool.
The Merseytram was intended to be open by 2008
The £170m financial package promised for Merseytram by ministers was pulled in November.
Merseytravel wants a High Court judge to order the government to hand over the money it originally pledged.
The passenger transport authority's case is expected to be decided at the hearing in London in the next few days.
Transport Minister Derek Twigg had said that the money would not be released because local councils had not agreed to fund any shortfall.
Lawyers have lodged four main charges in the case against the government.
These include a claim that it breached a commitment made in 2002 that £170m would be available for the scheme if certain conditions were met.
Merseytravel say the scheme's planning has cost £50m to date
Construction could start in March, with completion in 2009, if the judicial review is successful.
If the government's decision is upheld, Merseytravel wants to recoup money it has invested in the project over the last six years.
It had been hoped the first tram line from Liverpool city centre to Kirkby would be in place in time for Liverpool's year as European Capital of Culture in 2008.