Mick Lynch has accused ministers of torpedoing a deal, as tens of thousands of rail workers walked out on a fresh strike.
The boss of the Rail, Maritime and Transport union [RMT] claimed ministers were “undermining efforts to get a settlement” and had sunk an agreement in December.
However, transport secretary Mark Harper denied this, saying they had “done the opposite” and were trying to facilitate a deal.
Commuters faced fresh disruption on Tuesday as rail workers walked out in the dispute over pay, jobs and conditions.
RMT members will stage two 48-hour walkouts from Tuesday and Friday, while drivers in the Aslef union will strike on Thursday.
Lynch told Sky News: “What we keep hearing is the same stuff from the government across the sectors that they want to facilitate an agreement, but they don’t actually do anything.
“I met the rail minister on December 15 along with the companies. We have heard nothing tangible since then, we hear a few warm words and Mark Harper conducts himself in a pleasant way, in a good way, and that’s fine.
“What we need to hear now from the government is exactly what it is they are going to propose to us.
“They they got themselves into a position before Christmas, where we were making progress with the train operating companies, and on one Sunday afternoon before a set of strike action, they decided to torpedo those talks by putting in conditions in the documentation that they know that we and the other unions can never accept.”
Lynch alleged it was a “deliberate strategy” which had frustrated the train operating company executives as well as the unions.
Harper denied they had blocked a deal, telling Times Radio: “That’s simply not true.
“When I took over as transport secretary a couple of months ago, I met the trade union leaders including Mr Lynch. I said that we would play a role in facilitating the employers and the trade unions getting together.
“They’ve got to hammer out the detailed negotiations. I made sure that there was a pay offer that went to the RMT both from the train operating companies and also from Network Rail.
“That was, I think, a fair and reasonable offer in line with what most of your listeners in the wider economy will have got over the past year.
“That offer was accepted by two of the trade unions, the RMT recommended that it not be accepted. So we’ve actually made sure there has been an offer.
“We’ve done the opposite of trying to block a deal. We’ve actually tried to facilitate a deal and as I said in the new year it’s time for the RMT to get off the picket line around the negotiating table.”
Tim Shoveller, Network Rail’s chief negotiator, has said a deal to stop rail strikes is in “touching distance”.
“Some members are coming back to work, and we are seeing increasing numbers come back to work, but that’s not the way to resolve the problem or the dispute,” he told BBC Radio 4’s Today programme.
Passengers returning to work after the festive break are being warned to expect “significant disruption” with only a limited number of trains running.
The advice is to only travel if absolutely necessary, allow extra time and check when first and last trains will depart.
A department for transport spokesperson said: “Unions should step back from this strike action so we can start 2023 by ending this damaging dispute.”