It's well-known that even "friendly" or "allied" countries regularly spy on each other. Considering this, I started to wonder whether sub-national entities spy on each other too. Is there any precedent for this?
For a hypothetical, maybe the Texas Ranger Division plants a mole in the California Highway Patrol to leak California law enforcement-sensitive data to Texas intelligence officials, and California hires tech pros to hack Texas school servers to steal curriculum updates and pedagogical best-practices before they are made public. This could happen in non-US countries too, perhaps there is a young person right now beginning his career as a sleeper agent in the Ontario Ministry of Health with true loyalty to Nova Scotia and ready to activate on a coded signal to leak data or even commit sabotage.
Does this sort of thing ever actually happen, or is sub-national spying just not a thing?
In response to a comment by CGCampbell yes, interstate travel to obtain abortions could be relevant to this. With news that California intends to become a "sanctuary" state to shield out-of-staters from reproductive and gender oppression, it makes sense that one of those states might want to spy on Cali to find out which of their wayward citizens are receiving services there in order to craft the perfect extradition demands.
In response to a comment by User65535, I would be hesitant to allow cases where one administrative arm of a government "spied" on another administrative arm of the same jurisdictional government (e.g. the Ontario Ministry of Health spying on the Ontario Provincial Police). Normally, the political principle of "Checks and Balances" provides that governmental agencies can, and often should, keep tabs on what other agencies are doing. I could allow it in cases where the alleged spying went far beyond the agency's mandate rather than just consisting of some official taking their job a little too seriously and slightly horning in on the target agency's racket. I will omit military coups since they are somewhat common and easy to research.
In terms of what qualifies as true "espionage" versus simple information gathering or research, I would generally say that espionage necessarily involves acts that are physically, legally, or politically risky to the agent performing the act and/or the jurisdiction sponsoring it. For example, California sending young-ish looking California Highway Patrol officers into Nevada with forged Nevada residency documents with orders to fraudulently enroll in Nevada public high schools and gather intelligence on Nevada educational practices would most likely violate Nevada law, expose the agents to imprisonment by Nevada, and thus qualify as espionage. Sending agents to drive around other jurisdictions and document what they see happening on the street normally wouldn't qualify as espionage under this definition since no laws would be being broken and the political fallout of the discovery of this by the target jurisdiction would likely be minimal.