Ryanair has been accused of breaking electoral law over its campaign for the UK to remain in the EU.
According to reports by BBC News, the Electoral Commission says anyone intending to spend more than £10,000 campaigning around the referendum must register.
However the regulation around spending on the campaign may not be relevant to Ryanair as it is registered as a company in Ireland, BBC News adds.
The UK will vote on whether to stay in or leave the European Union on June 23. Ryanair pledged to spend more money than the limit but has not registered.
Reports claim the Vote Leave group has urged the commission to investigate. The low-cost airline hit back by calling the campaign “Leave loonies”.
Ryanair is alleged to have spent around £19,000 on the campaign to remain in the EU.
An Electoral Commission spokesman confirmed it had “received a complaint from Vote Leave regarding the campaigning activity of Ryanair at the EU referendum.”
“We are establishing the facts before determining what, if any, further steps to take,” it added.
Speaking to the Today programme on BBC Radio 4, a Ryanair spokesman said: “With less than four weeks to go, we will continue to work hard to help deliver a resounding Remain majority on 23 June – and ensure that the Leave loonies don’t ban low-fare air travel too.”