E-Z Pass do not operate in Ireland, so yes, almost certainly a phishing email. The former Easy Pass (Easy, no E-Z) are now operating as Easy Trip. E-Z Pass operate in the US.
A genuine unpaid toll notice will come from one of the official operators, and if you think about it, they're very unlikely to have your email address. Unpaid tolls in Ireland could only really originate from use of the M50 barrier-free toll, which is operated by eFlow.
I'm guessing there was an attachment? - If so, do not open it. Just opening it can be enough to compromise your system. The same applies if there was there a link to follow.