A phrase for: an underhanded malicious act that appears to be done in good faith

In Polish there's a phrase "podłożyć [komuś] świnię", literally "set up pig [under somebody]". It means performing an action that - while otherwise completely legal, seemingly neutral, and not apparently malicious, is extremely undesirable to somebody affected - and was performed for that very reason, to cause trouble to the affected.

It's related to "setting somebody up (to fail)", "giving them enough rope to hang themselves", "setting them a lose-lose scenario", "digging up dirt", etc, but with a special focus on the effect of a deliberate but seemingly arbitrary decision. Also, police "sting" operations sometimes happen to be this, especially if the target was originally reluctant to perform the "criminal activity".

Some examples:

• in understaffed branch of company you reserve holidays for yourself for a time for when your (disliked) co-worker planned some trip to an event they eagerly awaited; they will not be given time off with the division short-staffed by your absence.
• The disliked person has a court case with unrelated third party. You provide the third party with efficient court advice.
• Follow a faulty order to the dot, making sure to give credit for the disastrous outcome where it's due. Possibly even (unofficially) suggest that course of action in the first place.
• Your political opponent allegedly made a bad slip of bad judgment, did something legally ambiguous sometime in the past. Report that to authorities shortly before elections.

Are there idioms/phrases to describe this kind of action?

Solution 1:

To put a spoke in someone's wheel or just spoke his wheel is to materially damage a person's plans or progress. (Don't ask me why it's not spike or stick instead of spoke, there's debate about the origin of this seemingly strange phrase.)

put a spoke in somebody's wheel
(informal)

to make it ​difficult for someone to ​achieve something they had ​planned to do:
His ​letter really put a spoke in ​our ​wheel.

source: Cambridge Dictionaries Online

But I don't think English has a set phrase with all the connotations you are looking for. It's possible you could come up with your own phrase that people would understand. Something like plausibly deniable malice or ostensibly innocent malignance.

plausible deniability

... circumstances where a denial of responsibilty or knowledge of wrongdoing can not be proved as true or untrue due to a lack of evidence proving the allegation. This term is often used in reference to situations where high ranking officials deny responsibilty for or knowledge of wrongdoing by lower ranking officials. In those situations officials can "plausibly deny" an allegation even though it may be true.

It also refers to any act that leaves little or no evidence of wrongdoing or abuse.

source: uslegal.com

malice n.

1. desire to inflict injury, harm, or suffering on another, either because of a hostile impulse or out of deep-seated meanness:
   the malice and spite of a lifelong enemy.

source: dictionary.com

ostensible adj.

2 : being such in appearance : plausible rather than demonstrably true or real:
the ostensible purpose for the trip

source: Merriam-Webster

A related concept that may interest you is practicing strategic incompetence, which is intentional failure at tasks in order to relieve oneself of responsibility for them.

Another word that may be of use to you is Machiavellian, meaning (Merriam-Webster) suggesting the principles of conduct laid down by Machiavelli; specifically: marked by cunning, duplicity, or bad faith.

Solution 2:

It sounds like a spite:

• a malicious, usually petty desire to harm, annoy, or humiliate another person; malice.

• malevolence by virtue of being malicious or spiteful or nasty.

The expression is out of spite :

• with the desire to harm someone or something.
  • Jane told some evil gossip about Bill out of spite. That was not an accident! You did it out of spite.

The Free Dictionary

Solution 3:

Consider,

play a dirty trick on someone

play a trick on someone or play a prank on someone: to do a trick that affects someone. McGraw-Hill Dictionary of American Idioms and Phrasal Verbs

pull a dirty trick on someone

pull a trick (also, pull a stunt) [on someone]: to deceive someone; to play a trick on someone. McGraw-Hill Dictionary of American Idioms and Phrasal Verbs

screw someone over

: informal treat someone unfairly; cheat or swindle someone. OED

land [give] someone a low blow

low blow: an unfair blow McGraw-Hill's Dictionary of American Slang and Colloquial Expressions

For example, When my roommate moved out without a word of warning, leaving me to pay the entire rent, that was a low blow, or She wanted to win the argument, but bringing up his failed marriage was a low blow.

throw a [monkey] wrench in/into [the works]

: sabotage or frustrate a project or plans, as in The boss threw a monkey wrench into our plans when he said we'd have to work Saturday. This transfer of industrial sabotage—that is, throwing a tool inside machinery—to other subjects dates from the early 1900s.The American Heritage® Idioms Dictionary

Solution 4:

Consider the following idioms:

do the dirty on someone:

to ​behave unfairly towards someone, usually without ​their ​knowledge

(http://dictionary.cambridge.org/dictionary/english/do-the-dirty-on-sb)

do someone dirt:

to do ill to someone; to harm someone’s reputation.

(http://idioms.thefreedictionary.com/do+someone+dirt)

do a dirty trick on someone:

dirty trick: an unkind or aggressive trick

(WordNet)

In addition, the British idiom to queer somebody's pitch could work:

to spoil someone's chances of doing something
She queered my pitch by asking for promotion before I did.

For instance, you could use "queer the pitch" in your political opponent example.