彼の行為は法律に背いている。
tbd
What he's doing is against the law.
His action is against the law.
What he's doing is illegal.
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背く， 叛く， そむく
1. to run counter to, to go against, to disobey, to infringe
tbd
は
1. indicates sentence topic
2. indicates contrast with another option (stated or unstated)
3. adds emphasis
指示句子的主题；表示与另一选项（无论是否明确提及）形成对比；表示强调
に
1. at (place, time), in, on, during
2. to (direction, state), toward, into
3. for (purpose)
4. because of (reason), for, with
5. by, from
6. as (i.e. in the role of)
7. per, in, for, a (e.g. "once a month")
8. and, in addition to
9. if, although
tbd