Christopher Renehan, 38, who is seven months into a six-year term at Dubai Central Prison, began refusing food at 5am on Monday.
The father of two children last spoke with his family in Ireland on Tuesday evening.
"He's still in good form but that could change over the next day or so," said his father, Michael.
Renehan was the managing partner of a building company, Sire Contracting, and was jailed after late payments from a client caused cheques that he had written to contractors to bounce.
The hunger strike "was his final option as he was getting no joy through the courts", said Mr Renehan. "His wife and children are very upset.
"I'm going to give it until early next week and then I'm going to have to talk him out of it. We don't want anything to happen to him."
Radha Stirling, the founder of the organisation Detained in Dubai, said the strike was important for Renehan's case and the wider issue of financial crimes.
"When starting business in Dubai, a local Emirati sponsor is required. While some of these relationships have been positive and prosperous, when greed gets involved, it can end in prison. When a local sponsor accuses a foreigner of a crime (breach of trust, fraud, embezzlement etc.), he is likely to be believed and the foreigner is likely to be successfully prosecuted. A partnership is open to abuse and many a client has found himself set up by a business partner, once a trusted friend.
Christopher Renehan and his wife informed us that they recently discovered associates of their local sponsor, have been seeking the invoices to the government departments to be paid directly to them, meaning Christopher would remain in prison for the full duration of his sentence, unable to repay the corporate debts personally.
Where such little evidence is required to secure a conviction and Court hearings taking as little as 20 minutes, even the most ethical and respected individual can find himself serving a lengthy sentence because “someone” has pointed the finger."
Radha Stirling, CEO and founder of Detained in Dubai - full article "Christopher Renehan jailed over bounced cheques in the UAE"
The John Murray Show RTE1 in Ireland interviews Radha Stirling from Detained in Dubai, regarding Christopher Renehan's incarceration in Central Dubai Prison over bounced cheques. Full story can be found on the Detained in Dubai website.