This is unusual not only because of the possible impact on the Northern Ireland peace treaty, but because it's an agreement that was only just made by the same government. Which makes the whole process look particularly stupid and insulting.
It's also the deliberateness that has upset people - breaching a complex agreement inadvertently is very different from setting out to do it deliberately.
airbus state aid is the biggest recent example: knowingly providing unlawful subsidy against WTO rules
the EU ignored its WTO state aid comittments when it suited it, and now is trying to force a much much stronger version of the rules that it routinely breaks, onto the UK
It's also the deliberateness that has upset people - breaching a complex agreement inadvertently is very different from setting out to do it deliberately.