It isn't. There are a number of occupations where there is no right to strike, indeed it is unlawful to do so. These include the police, armed forces, prison officers and others where they technically could but could be seen to be in breach of their professional codes of conduct if they did, such as nurses and doctors (because it could be seen as counting as an omission of care if any harm was caused by the action, it's why the doctor's strike didn't really get very far).
In the UK!
The Netherlands has TUs for the armed forces. The police can and do strike in countries such as France and Italy which is one of the reasons why there are multiple police forces, some paramilitary (eg Spanish Guardia Civile, Italian Carabinerie).
In the UK there were serious proposals a few years ago for the Police Federation to take legal action over the current ban as a violation of Human Rights.
The other way round. An organisation or an individual might challenge the addition of a no-strike clause to contracts, and the courts would decide whether or not it conflicted with the Human Rights Act or any other legislation. If we've left the EU and the Human Rights Act no longer applies here that might affect the outcome.
I see a big difference between striking over an issue of pay or working practices which is in dispute in some way, and striking because the employer won't give an assurance that they will never propose a change to a system which is already widely in use. The resulting disruption to passengers seems likely to create support for restricting the right to strike.
Oh Lord, where do I begin to address the numerous errors in this posting?
The Human Rights Act is UK legislation which implements the European Convention on Human Rights (ECHR, which was de facto written by Sir David Maxwell-Fyfe a former UK Attorney General appointed by Winston Churchill) into UK law.
The UK was an initial signatory of the ECHR (which is absolutely nothing to do with the EU). The ECHR is overseen by the European Court of Human Rights based in Strasbourg (which despite rants by the Daily Mail and Express has absolutely nothing to do with the EU).
If the Human Rights Act is repealed the Tories have stated that it will be replaced with a British Bill of Rights. If UK remains in the ECHR that will have limited tending to zero effect in practice. Indeed, there is a legal argument that to do so may actually lead to an increase in cases going to Strasbourg, because the ECHR protects the right to a remedy (Article 13). If we remove the remedies available under the Human Rights Act then more cases may end up being admitted to the court in Strasbourg.
If UK leaves the ECHR, something only the Tory rightwing have mooted and moderate Tories have vowed to oppose, things might be different. However in Scotland, the First Minister, Nicola Sturgeon, has already indicated that the Scottish parliament would refuse to consent to any change to the devolved application of the ECHR which is already protected in the Scotland Act 1998. In Northern Ireland, change to the human rights structure becomes even more problematic as the ECHR plays a foundational role in the peace process. To remove the ECHR framework would be in direct breach of a legally binding international agreement that the UK entered into with Ireland. In Wales, the Welsh Assembly have already forged ahead with legislation which actually increases the protection of human rights by incorporating a duty to have due regard to the UN Convention on the Rights of the Child. See any issues???
Oh, if UK does leave the ECHR that leaves us in the company of the "enlightened" regime (ie effective dictatorship) of Belarus. All of the rest of Europe (47 states) are members.