Juncker and Brussels team spent Â£24,000 on 'air taxi' for one-night trip to Rome
Documents released by the Commission after a two-year battle with human rights group Access Info revealed that the 28 commissioners accumulated a near-500,000 euro (Â£452,770) expenses bill in two months last year.
Among the papers were claims for so-called "air taxis" - private jets which commissioners are supposed to charter when there are no commercial options available.
Mr Juncker, as part of a nine-person delegation, chartered one such jet for a trip to Rome on February 25 and 26 2016 at a cost of 26,351 euros (Â£23,862) - described by Nigel Farage as "outrageous" and "clearly over the top".
According to the website for Brussels Airport, there are currently six daily flights between the Belgian capital, home to the Commission headquarters, and Rome, while there is an extra flight from Brussels South Charleroi airport.
Commission deputy chief spokeswoman Mina Andreeva said the private jet was chartered by Mr Juncker and the delegation because there was "no viable commercial plane available that would fit the president's agenda" and stressed the 2,927 euro (Â£2,650) per person cost of the flight.
At the Commission's regular midday press briefing, Ms Andreeva also described flights on "air taxis" as "hard work", which includes "reading documents with your files and marking them", adding: "So I think you will be disappointed as to the travelling experience."
Asked if the cost of the flights would be included in the so-called "divorce bill" Britain is being asked to pay to settle budget commitments, she replied: "The flights are part of the yearly budget that the Commission has and that is audited and there is an administrative section so it's within this section that we can spend travel expenses and this is outlined in the yearly budget.
"As to a Brexit bill, there is no Brexit bill; there are outstanding commitments that need to be paid and this is part of the negotiations, but the travel costs are governed by our rules and are part of the annual budget which again is publicly available."
Commenting on the revelations, former Ukip leader and current MEP Mr Farage said: "Outrageous! Juncker spending 27,000 euro on a private jet at taxpayers' expense is clearly over the top especially when many normal flights are available.
"I suppose these junket expenses are all part of the make-believe 'Brexit bill' which these commissioners have plucked out of thin air and trying to extort from our Government."