Police said the couple were murdered by an upper caste grocer on Thursday when they told him they needed time to pay for biscuits they had bought from him.
The grocer has been arrested.
Dalits, formerly known as untouchables, form the lowest rung of India's caste hierarchy.
Police told the Press Trust of India news agency the incident took place in Mainpuri district early on Thursday as the couple were on their way to work.
They were stopped by Ashok Mishra,  the owner of a village grocery, who demanded that the couple pay the money for three packets of biscuits that they had bought for their three children a few days ago, reports say.
The couple reportedly told him they would pay after they received their daily wages later in the evening.
"While Mishra kept shouting for the money, the couple started walking towards the fields. Mishra then ran to his house nearby and returned with an axe. He hacked Bharat repeatedly and then attacked Mamta who was trying to rescue her husband. The couple died on the spot," Nadeem, a local villager, told The Indian Express newspaper.
The Dalit community in the village have blocked roads and protested over the incident.
Earlier this month four low-caste Dalit men were assaulted by cow protection vigilantes while trying to skin a dead cow in western Gujarat state.
Many Hindus consider cows sacred and the slaughter of the animal is banned in many Indian states.
In March, a Dalit man was murdered for marrying a woman from a higher caste in the southern state of Tamil Nadu.
The woman's father handed himself in and admitted to carrying out the attack on a busy road in daylight, police said.
A man from India's Dalit community has been beheaded and his wife hacked to death after a row over a 15 rupees (22 cents; 16 pence) debt in Uttar Pradesh state.