Prime Minister Enda Kenny warned Monday that Ireland's sovereign debt could be downgraded by rating agencies if the country rejects the EU's fiscal pact in a referendum on Thursday.
Kenny's comments came as the first votes in Ireland's referendum were cast on five remote islands off the northwest coast ahead of the mainland ballot.
"We have had a number rating agencies already indicate that if the people were to turn down the fiscal stability treaty, that a downgrading of the country would follow," Kenny told reporters.
"When we are in the business of being serious with companies abroad who want to know the kind of country that we are and what it is that we offer, why should we inflict a lack of confidence on our own belief and on our own country?
"These people want to know what the future is going to hold for them if they invest serious money in Ireland," he added.
Ireland relies on exports to boost its debt-ridden economy and some 75 percent of its trade involves goods and services from foreign-backed companies which have set up operations in the country.
Ireland's referendum is expected to be the only plebiscite in the European Union on the fiscal pact, which is designed to strengthen the euro currency through tighter oversight of public finances.
People living on Irish islands in the Atlantic Ocean off Counties Donegal, Mayo and Galway traditionally vote early, in case bad weather delays getting the ballot boxes back to count centres on the mainland.
The Irish environment ministry, which administers referendums, said 765 people living on five islands off Donegal would be able to cast their votes on Monday, followed by 194 on three islands off Mayo on Tuesday.
Some 1,164 voters on five islands off Galway can vote on Wednesday.
Four opinion polls at the weekend put the "yes" camp ahead by between 57 percent and 60 percent but they also showed many voters were still undecided.
Ireland was forced to seek an 85-billion-euro ($106-billion) bailout from the EU and International Monetary Fund in 2010.
Under the fiscal pact, any country that fails to ratify will not be allowed access to the European Stability Mechanism, the permanent EU bailout fund that comes into force in July.
The Irish vote will be watched closely as the republic has previously sent shockwaves through Europe on treaty plans.
It voted twice before passing two fundamental EU treaties, the Nice and Lisbon accords.
If Irish voters reject the fiscal pact, however, it would only affect Ireland and its access to EU funds and not hold back other member states.
The pact, drawn up in response to the eurozone crisis, obliges countries to enshrine in national law a so-called "golden rule" to balance budgets or face automatic sanctions.
Some 3.1 million people will be eligible to vote in the mainland on Thursday. Votes will be counted on Friday.