Mick Lynch has accused the government of “blocking” a deal to resolve the railway strikes.
The general secretary of the Rail, Maritime and Transport union (RMT) said on Monday there had been “unprecedented level of ministerial interference” by ministers.
The government has denied claims by unions that it is now the main stumbling block to ending the bitter dispute.
A fresh wave of strikes this week will cause travel chaos as RMT members and drivers in Aslef stage walkouts.
Around 40,000 RMT members on Network Rail and 14 train operating companies will take action on January 3, 4, 6 and 7, shutting down most rail services across the country.
A one-day strike on Thursday by drivers will cripple services and passengers have been urged to only travel if necessary.
The RMT said that despite its best efforts over the Christmas period, rail employers have not arranged any formal negotiations to resolve the dispute.
A statement said: “Both Network Rail and the Rail Delivery Group are being directly blocked by government ministers from producing an acceptable proposal on job security, pay and working conditions.
“RMT remains available around the clock for talks so all parties can come to a negotiated settlement.”
The RMT said the position was in stark contrast to other areas of the railway where the Department for Transport does not have a mandate.
The union said it has secured deals with Scotrail, Transport for Wales, contracts on Eurostar and areas where the railway is under the control of metro mayors.
Lynch said: “The government is blocking the union’s attempts to reach a negotiated settlement with the rail employers.
“We have worked with the rail industry to reach successful negotiated settlements ever since privatisation in 1993 and we have achieved deals across the network in 2021 and 2022 where the DfT has no involvement.
“Yet in this dispute, there is an unprecedented level of ministerial interference, which is hamstringing rail employers from being able to negotiate a package of measures with us, so we can settle this dispute.
“We will continue our industrial action campaign while we work towards a negotiated resolution.”
On RMT strike days, around half of the network will shut down, with only about 20% of normal services running.
Trains that do run will start later and finish much earlier than usual – with services typically running between 7.30am and 6.30pm on the day of the strike.
The train drivers’ strike on Thursday will affect 15 operators and will result in even fewer services running, with some companies running “very significantly reduced” timetables.
A Department for Transport spokesperson said: “Passengers have rightly had enough of rail strikes and want the disruption to end.
“The government has demonstrated it is being reasonable and stands ready to facilitate a resolution to rail disputes. It’s time the unions came to the table and played their part as well.
“Inflation-matching pay increases for all public-sector workers would cost everyone more in the long-term – worsening debt, fuelling inflation, and costing every household an extra £1,000.
“Unions should step back from this strike action so we can start 2023 by ending this damaging dispute.”