According to an article in the Guardian the Maldives are going to ban Israelis from visiting.
According to a quote in wikipedia...
International law posits that no person may be punished for acts that he or she did not commit. It ensures that the collective punishment of a group of persons for a crime committed by an individual is forbidden...
So, if both of these statements are correct, is the Government of the Maldives breaking international law?
Every country has a sovereign right to decide who's allowed to enter it. There's no such thing as "international law", only international treaties and conventions. There's no convention or treaty that requires any country to allow citizens of any other country in. The ability to enter a foreign country is a privilege, not a right.
The Maldives have no diplomatic relationships with Israel, and will not be the first, or the only, Muslim country to not allow Israelis to enter (in fact they have only been allowing Israelis to enter since sometime in 1990s).
The Global Commission on International Migration published a paper by Colin Harvey and Robert P. Barnidge, Jr. called "The right to leave one’s own country under international law" in 2005. In it, the argument is that international treaties give humans the right to leave their country of origin. However, the author nowhere argues that anyone has a right to enter any country. In fact, the author repeats again and again (and cites where applicable) that there is no general right to enter:
The existence of a right to leave does not entail an automatic right to enter other states.
The emphasis is on channelling free movement into its legally permissible forms and thus ensuring that states are able to retain a sufficient measure of control over who is permitted to enter their territory
There is an obvious disjuncture with respect to the right to leave in the fact that there is no corresponding general right to enter another state, which presumably would be a state of the migrant’s choosing. [...] The right to leave still must confront the fact that there is no general right to enter other states for most of the world’s migrants.
A right to enter is generally found on various grounds: you might have a Visa, you might be from a state with which the country has a bilateral free movement treaty or you might qualify for asylum. All of those and more can establish a particular right to enter a country, but there is no such right for all the population of earth. As an inversion, that means that international law allows a blanket ban on entry based of origin, provided that the destination country can justify it under its own laws.
Not granting visa and banning ordinary entry from a state with which you don't have diplomatic relations is more normal than not: During both world wars, the entry of people with German passports to several countries was banned but for those seeking asylum once war was declared. Likewise, people from countries Germany was at war with were not allowed entry during the war, unless they were members of the Red Cross or Diplomats.
At its very core, a punishment is a denial of a right, which is decidedly different from revoking a privilege. While technically in both cases it has a negative impact on the recipient, these are judged in very different ways.
There's a perceptional difference between doing something and choosing to not do something. It all depends on what the baseline is and whether your actions are willfully deviating from the baseline.
Collective punishment refers to actively doing something different from the baseline (i.e. willfully creating a negative consequence), and applying this to a large demographic based on a justification that applies only to a subset of that demographic.
The implicit baseline here is "live and let live", i.e. this wouldn't be happening except that you chose to enact this punishment, and the way you are treating this demographic is not how you treat everyone else.
In terms of entering a nation's borders, the baseline is that no one is entitled to enter (other than its own citizens). Access is only granted on a basis of active consent from that nation. Therefore, a nation not letting in a specific nationality is not deviating from the baseline. It's exactly on the baseline, with no additional privileges being granted.
Using a simple analogy, just because I give my friends a key to my house and tell them they're free to come over when they want to, does not mean that I am "punishing everyone else" by not also giving them a key to my house. That's not how this works. The baseline is that no one except me (and any other people living here) have access to the house. Extending that privilege to others does not bind me to extending it as a right to just anyone.
In order for you to claim that banning a nationality from entering another nation is collective punishment, it would require you to first argue that everyone is inherently entitled entrance to this nation (which would then be the baseline), because that would then allow you to argue that disallowing a certain demographic from entering said country would be creating a punishment that deviates from the baseline.
This is not the case, and any country that were to default to entitling every person unbridled access to their borders as the default effectively does not exert any real control over its own borders.
It's not impossible for a nation to do so, but it is decidedly unlikely that a nation would ever choose to do so because of the obvious drawbacks with no real benefits.
So, no, not being allowed in a country is not the same as being punished.
Punishment is the withholding of something that you have and/or are entitled to have/acquire. This may be your freedom (through imprisonment), your assets (fines, seizures), or something else (ice cream after dinner, use of the executive lounge).
Presence in a country that you are not currently in is by definition something you don’t have, and for nearly all countries it is something that only citizens are categorically entitled to. (A few countries like Mexico recognize a universal right to enter and pass through, though not to reside.) For non-citizens, it is a privilege that can be acquired only by explicitly being granted. Denial of a request for a privilege does not in any way constitute punishment.
