Greg Wilkinson took 10 packs marked "grown in the West Bank" from the Swansea Marina branch of the supermarket — then wrote to the company's boss with his name and address to tell him what he had done.
He said he "confiscated" the dates because he believed they had been produced on land illegally occupied by Israel. And he said he was prepared to face the consequences of his actions in court.
Mr Wilkinson, from Brynmill, Swansea, said: "I took this action because I have reason to believe that the dates come from illegal Israeli settlements in occupied Palestine.
"The dates are labelled Grown in the West Bank, where the main date-growing area is the Jordan Valley, a military zone under Israeli occupation.
"Occupation and settlements are illegal under international law.
"It is not acceptable that Tesco should sell goods from stolen land, nor that the 'West Bank' label leads customers to believe they are buying legitimate Palestinian produce.
"If Tesco can satisfy me they are not from illegal settlements, it will be refunded."
The 72-year-old said he was spurred into action by the current violence in Gaza, where Israel has launched a major military campaign to try to stop missile and rocket attacks from the area.
According to Palestinian sources, the number of people killed stands at more than 500, with some 2,500 wounded — but these figures cannot be independently confirmed.
"I am angry and upset over what is happening in Gaza and I considered what action I could take," said the former journalist, who has also worked as a builder, a community worker and Llanelli smallholder. "I don't know what the reaction of Tesco will be — whether I will be referred to the police or whether they will remove these dates from their shelves.
"I did this in the full knowledge of what I was doing — and if it comes to court, I won't pay any fine."
The campaigning pensioner has written to Sir Terry Leahy, the chief executive of Tesco, to tell him what he did, and why.
The dates were worth £29.90, and Mr Wilkinson said he gave them away or sold them at last weekend's rally in support of Palestine in Swansea's Castle Square.
The money raised from selling the stolen dates — plus donations from well-wishers — came to £120, which Mr Wilkinson said he had donated to Oxfam and Islamic Relief's Gaza emergency appeal.
A spokeswoman for Tesco said an investigation into the incident was underway.
She added: "We understand that many customers have strong views, from a wide variety of positions, about the situation in the Middle East. Therefore, we clearly label the origin of our products so that our customers are able to make informed choices about what they wish to purchase.
"In relation to products from the Occupied Territories, we label all our products from there in accordance with EU and UK government guidelines, which state that produce from this area should be labelled clearly with a regional indication.
"This means it will state on the packaging if the product is from Israel or the West Bank, allowing our customers to make an informed choice about whether they wish to buy products from this part of the world."