IAG has said it is considering launching a legal challenge against the UK government's 14-day quarantine rule for incoming travellers.
The International Airlines Group is one of the biggest in the world and owns British Airways and Aer Lingus.
Willie Walsh, the Chief Executive of IAG, told Sky News that there had been no consultation with the industry prior to the legislation being brought in, and that the new rules would "torpedo" British Airways' chances of flying in July.
"We think it is irrational, we think it is disproportionate and we are giving consideration to a legal challenge to this legislation," Walsh said.
Meanwhile, Ryanair has called on Taoiseach Leo Varadkar to scrap Ireland's visitor quarantine restrictions from the end of the month.
It comes as the European Commission called on EU members to lift EU border restrictions by the end of June.
In a statement, Ryanair’s CEO Eddie Wilson described the quarantine restrictions as "ineffective" and called on the Taoiseach to follow the EU advice.
"If the EU is ready to reopen, why does Ireland insist on adding obstacles with an ineffective and useless visitor quarantine?" he said.
