Five Labour metro mayors are preparing to take legal action in a bid to stop the “rushed” planned mass closure of railway station ticket offices.
They launched a three-week consultation on the measure.
Industry body the Rail Delivery Group (RDG) insisted ticket office staff will be moved onto station platforms and concourses to “modernise customer service”.
But Mr Burnham said: “These closures will affect over 2,000 jobs.
“It’s just not the case that this is about redeploying staff. This will be a serious reduction in the level of support available to people when they are travelling.
“It will further erode what remains of trust in travelling on our trains and we think it is the wrong move at the wrong time.
“We’re very worried that these plans are being railroaded through.
“Today we are confirming that as five mayors representing millions of people across England, we are fighting back.”
The other mayors involved are: Tracy Brabin of West Yorkshire; Steve Rotheram of Liverpool City Region; Oliver Coppard of South Yorkshire; and Dr Nik Johnson of Cambridgeshire and Peterborough.
Mr Burnham said the “rushed” consultation “does not provide a legal basis” for closing ticket offices, meaning it “should be declared null and void”.
He went on: “Section 29 of the Railways Act 2005 sets out a very clear and detailed process which must be followed if a train operating company proposes to close a station or any part of a station.
“That process has simply not been followed in this instance.
“For instance, it requires a 12-week consultation. Of course that is nothing like what is being currently undertaken by the train operating companies.”
The mayors intend to send a pre-action protocol letter to operators in their areas, setting out why they believe closing ticket offices in this way is unlawful.
A spokesperson for the RDG said: “All train operators are complying with the consultation process as set out in the Ticketing and Settlement Agreement.
“They include proposals which, across the network as a whole, would see more staff on concourses and ticket halls to help passengers than there are today, helping with a whole range of needs, from buying tickets to journey planning and helping with accessibility needs.
“We encourage anyone who wants to find out more to contact their local train company, or submit their views to independent passenger watchdogs Transport Focus or London TravelWatch.”