The airline has accused Ireland of "lagging behind Europe's Covid recovery".
Ryanair has called on Transport Minister Eamon Ryan to explain why he is failing to reopen the island of Ireland to air travel.
The airline wants Ryan to clarify why Ireland has not begun issuing EU Digital Covid Certificates (EUDCC) to its vaccinated citizens yet.
According to the European Commission's website, 18 European countries are now issuing the certificates.
However, while Ireland is said to be "technically ready to connect to the EUDCC gateway", it has not yet rolled out the certificates to the public.
After Ryanair Chief Michael O'Leary recently slammed Eamon Ryan as “without doubt one of the worst transport ministers we’ve had in our history”, the airline has now accused Ireland of "being an outlier and lagging behind Europe's Covid recovery".
"Ireland, an island on the periphery of Europe, has had its connectivity destroyed by this government’s mismanagement of the Covid-19 lockdowns and reopening," a Ryanair statement read.
"UK visitors (who are the most vaccinated in the EU) are still required to quarantine if they fly here, but they can drive across the border from Northern Ireland with no restrictions whatsoever!!
"Meanwhile, Ireland has still failed to roll out the EU Digital Green Cert (which is ready to switch on today) despite the fact that 18 other EU countries are now issuing the Digital Green Cert to their vaccinated citizens.
"Ireland’s Transport Minister continues to delay this urgent initiative while he dithers over how to include negative PCR tests and/or citizens who have contacted Covid but have recovered."
Highlighting Ireland's low Covid-19 hospital figures, Ryanair’s Eddie Wilson said Ireland was continuing to delay the recovery of aviation and tourism due to "bogus and non-medical fears about a Delta variant in the UK which is not resistant to vaccines".
He added: "It is time for Minister Ryan to wake up and roll out the EU Digital Cert at least for those Irish citizens who have been double vaccinated, and this can be switched on today! Negative PCR tests and Covid recoveries can be added later.
"It is bizarre and inexplicable that Irish vaccinated citizens are not free to travel without restrictions to/from the EU, even when Ireland has fully vaccinated all of its vulnerable groups, and our Covid case numbers continue to dwindle to nothing, and even these declining case numbers, are occurring in the under 35 year old category who are mainly asymptomatic and don’t suffer serious illness or hospitalisations."
Wilson urged Ryan to "take immediate action" to open the UK Common Travel Area and switch on Ireland’s EU Digital Green Cert "well before 1 July.”
Speaking on Wednesday, Health Minister Stephen Donnelly said he was "concerned" about the emerging Delta variant in Ireland.
He said: "The concern I have is that we are now surrounded by the Delta variant. We know it's significantly more contagious. We believe it is a lot more severe, two to two and a half times more likely to hospitalise somebody... and we know that at least for the first dose, it is less susceptible to vaccines, so this is a very, very serious variant."
While non-essential international travel is set to return on 19 July, Minister of State Ossian Smyth said on Tuesday that it's not guaranteed current travel restrictions will be lifted on that date.