Ryanair says it plans to cut up to 1,000 flights between Ireland and the UK during the months of August and September because of the ongoing travel restrictions.
The airline claimed this would result in more than 200,000 fewer passengers in Cork, Shannon, Knock and Kerry airports.
It again criticised the ongoing quarantine restrictions in Ireland, which require passengers arriving into the country to fill in a locator form saying where they intend to spend the following fortnight self-isolating.
It said the restrictions remain despite the UK and Northern Ireland opening up air bridges to most EU countries last week and the border between Ireland and Northern Ireland remaining open.
This situation it stated is leading to unrecoverable losses being sustained by the economy here.
"It makes no sense, when governments all over Europe have opened up EU flights since 1 June and removed travel restrictions on intra-EU travel, that the Irish Government continues to treat countries like Germany, Denmark and Greece as if they were suffering similar levels of Covid as the USA, Brazil and India," a spokesperson said.
"We call on the Irish Government to remove all travel restrictions between Ireland and the EU … as a matter of urgency, so that Ireland's hotels, guest houses, restaurants and other tourism providers can recover their business and minimise job losses before we reach the downturn winter period."
However, the Government has continued to stick by its travel restrictions policy, arguing that if people travel abroad for non-essential reasons it will increase the risk of Covid-19 cases being brought into the country.
Many public health experts have expressed great concern about the possible risks posed by foreign travel to the progress made by Ireland in reducing the levels of the virus in the community.
8% of Ryanair's flights arrive in or depart from Ireland.
Next Monday, the Government is due to publish a so-called "green list" of countries that it will be safe to travel into Ireland from without the need for quarantining.