Mick Lynch has claimed that Tory plans to introduce anti-strike legislation showed the UK Government had "lost the argument" on pay.
The Conservatives are considering measures which could allow employers to sue unions and sack workers if they did not provide a certain level of service.
It comes as RMT members employed by Network Rail take part in their second 48-hour strike of the week.
Train drivers in England also walked out on Thursday, affecting cross-border services to Scotland.
Lynch, the RMT general secretary, claimed Tory ministers were more interested in trying to "close down the unions" than resolving the dispute over pay.
He said: "What this is a symbol of is that the government are losing the argument. They’ve lost the argument on austerity and pay, and the state of our national public services.
"And instead they want to close that argument down by closing down the unions and stopping us from campaigning against poverty."
Lynch also said that the government and rail companies were "incompetent" and did not know how to run a railway service.
He said: "The railway service is in desperate straits.
"The companies that run it and the government that oversees it have shown that they are incompetent and incapable of understanding the railway and running the railway on a daily basis.
"When we are not on strike, the passengers are told, in this station and every other station, that due to shortages of staff trains aren’t running.
"At the same time, they say to me at the negotiating table that they want to make thousands of your members redundant.
"So, there is something desperately wrong with the way this railway is being run. But there is something desperately wrong with the way all public services are being run, and that’s why the workforce in these services are in rebellion now."
Pat McFadden, Labour's Shadow Treasury minister, warned the proposed laws wouldn't impact the current strikes.
He also accused the the Conservatives of playing political games instead of trying to find a solution.
McFadden told the BBC: "The Government, by reaching for legislation in the middle of this series of disputes, is striking a pause when it should be striking a deal, and the way out of this current series of disputes is to negotiate, not to legislate.
“No-one wants to see these strikes, they are causing ongoing significant disruption for the public.
“The way to resolve them at the end of the day is to negotiate a deal that will get the railways running again, get the nurses back to work and get the people back to work in the other sectors where industrial action is taking place.
“This legislation, even if it was enacted, it wouldn’t have an impact on these current disputes, and that’s been admitted by the Transport Secretary of State himself."
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