I've read that
Videos and pictures of Spanish police forces getting people down from the top of the [Melilla] fence by all means possible, including violent use of force, began to flood the news. News outlets and videos showed what local NGOs and all kind of organisations had tried to make public for years. The Spanish Government reacted by amending the Aliens Law (Ley Orgánica 4/2000) through a controversial new provision added to the Citizens Security Law (Ley Orgánica 4/2015). [...]
Against the concerns of several international organisations, such as the Council of Europe or UNCHR, and NGOs, such as Amnesty International, the Spanish Government converted push-backs into lawful “rejections at the border” by virtue of a law amendment. [...]
The Spanish Constitutional Court will rule on the Citizens Security Law, including the “rejections at the border” provision, in the near future. The decision was awaiting Strasbourg judgement.
It's not too clear what the latter is, but probably it is referring to the N.D. & N.T. vs Spain case, which actually came on the side of Spain (not illegal to push back migrants trying to force a border crossing en masse, if there's [even a remotely plausible] legal process to cross the border.)
But what exactly does the “rejections at the border” provision in the Spanish law say (in translation)?