Haryana was created out of Punjab in 1966 on linguistic lines. The two states share a capital, a high court, a governor for long periods, a river system and a border that is disputed in places.
The disputes are specific: Chandigarh, which was to go to Punjab and has not; the Punjabi-speaking areas left in Haryana, which Punjab claims; the Satluj Yamuna Link canal, which Haryana wants completed and Punjab will not complete; and the sharing of the Bhakra system's water and power.
Culturally the border is soft. The Powadh dialect runs across it. Families are related across it. The agricultural system is identical and the two states farm, procure and burn stubble the same way.
During the 2020 to 2021 farm protests the two states' farm unions worked together, and Haryana villages fed and housed Punjab's convoys on their way to Delhi, which was noted at the time as unusual.
The institutional dispute is sixty years old and the social relationship is not in dispute at all.
The Punjab and Haryana High Court sits at Chandigarh for both states and for the union territory, with one bar and one roll of advocates. Haryana has asked more than once for a high court of its own, but Punjab has not agreed and the court remains shared.
The Bhakra Beas Management Board runs the dams and allots the water and the power between Punjab, Haryana, Rajasthan, Himachal and Chandigarh, and its members are appointed from outside all of them. Who sits on it is itself a recurring quarrel.
Haryana passed Punjab in income per head in the 2000s, largely on Gurgaon and the industry along the Delhi road, and the half that was carved out as the poorer one is now the richer. Nothing in the constitutional argument between them has caught up with that.