Can a non-European simply buy their way into the Schengen Area? Or even pay to become a citizen of an EU country?

That's exactly what so-called golden visas are for — and Portugal is one of the countries that offers them. Anyone who invests at least €250,000 ($285,000) can first obtain a residence permit and, later, if they choose, even apply for a Portuguese passport.

The catch is that the government has recently changed the rules, and many people who have been waiting years for the residence permits they were promised are now planning to take legal action.

Golden visas — much like those US President Donald Trump has proposed for $1 million — are available in several EU countries, including Greece, Italy, and Latvia. In exchange for investments ranging from €50,000 to €500,000, applicants are supposed to contribute to the host country's economy. At least that's the theory.

However, these programs have long been controversial because they can attract people with questionable backgrounds — or even criminal ties — who many would rather not see living in their country and, by extension, gaining legal access to the European Union.