Private companies can quietly sue governments where changes in legislation adversely affect their profits. Even if those changes were implemented to support basic human rights iStock

It is Human Rights Day on 10 December, the occasion on which we commemorate the UN's adoption of the Universal Declaration of Human Rights.

Many will use the day to reflect on the human rights abuses that still occur around the world, such as war crimes, the plight of refugees, the cases of state-sponsored torture, the restriction of individual liberties, and many more.

But for me, it is a day to focus on a less well-known but more insidious threat to human rights – the Transatlantic Trade and Investment Partnership (TTIP) and the other so-called "free trade deals" around the world.

TTIP is currently being negotiated by the EU and US, despite numerous calls for it to be stopped, including a petition of over three million EU citizens. It is the largest bilateral trade deal of all time and seeks to promote trade by reducing regulatory barriers. TTIP won't see anyone tortured or incarcerated but its slowly creeping threat could undermine human rights in a broader and longer-lasting way than any Middle Eastern dictator.

This is because TTIP is all about the rights of investors and nothing to do with the rights of individuals. At the heart of TTIP and other such trade deals are the so-called Investor-State Dispute Settlements.

These ISDS provisions involve behind-closed-doors arbitration panels ruled not by independent judges but by corporate lawyers with vested interests in the corporations they serve. The ISDS allow private companies to sue national governments where changes in government legislation adversely affect their profits. And time and time again, in ISDS cases around the world, it has been shown that it is the rights of these investors that trump human rights every time.

Let's take one of the most fundamental human rights as an example – the right to water and sanitation. In a case that made it clear that investor rights were more important than human ones, earlier in 2015, the Argentine government was ordered to pay $405m (£267m) to a private water and sewage provider. The government's crime? That it had frozen water rates for a number of years to keep it affordable during a time of financial crisis.

How about another basic universal human right, the right to health? ISDS cases have shown time and again that public health comes second to corporate rights under such deals. Such is the case with Swedish energy company, Vattenfall, which sued the German government for billions of dollars over its decision to phase out nuclear power due to public health concerns in the wake of the Fukushima disaster.

Similarly, tobacco giant Philip Morris has used ISDS to sue the Australian government for introducing plain cigarette packaging. There have been hundreds of similar cases being heard behind closed doors around the world and many, if not most of them are found in favour of investors, although we don't know exact numbers because even the outcomes are often kept secret.

But ISDS isn't the only way TTIP will erode our rights. An attack on several human rights is enshrined in the very principle of TTIP, which is to remove the "regulatory barriers" to trade – "barriers" such as food and environmental safety laws. By reducing EU food safety and environmental laws to US levels, TTIP could open the door to more genetically modified ingredients in our food, to beef containing growth hormones linked to cancer, and a host of currently banned chemicals and pesticides.

The right to privacy is also under threat through an attempted easing of data and internet privacy laws. In fact, so many human rights are under threat that earlier in 2015, a number of UN experts felt the need to voice their concerns. These included fears over "rights to life, food, water and sanitation, health, housing, education, science and culture, improved labour standards, an independent judiciary, a clean environment and the right not to be subjected to forced resettlement". Quite a few then.

Even the continuation of the negotiating process in the face of such public concern trammels two of our basic human rights: the right to participate in government and the right to protest. EU citizens have been given no say in what goes into TTIP nor even over whether it will ultimately be agreed. Without democratic participation, there remains only protest. But even that avenue has been sealed off.

The petition against TTIP should have triggered a response from the European Commission once it reached a million signatures, becoming a so-called European Citizens' Initiative – the only means by which EU citizens can directly hold the EC to account on policies. However, the EC declared the petition didn't count as such an initiative thus muzzling any form of effective protest against the negotiations.

So let's commemorate Human Rights Day not just by considering the more obvious abuses. We should also take the time to think about the quieter, more insidious violations. These are the creeping tendrils of corporate power that behind closed doors are going quietly about the business of limiting our freedoms. After all, it is the unseen disease that often does the most damage.