A leading leftwing politician has sparked a row in Germany by proposing the rail operator Deutsche Bahn scraps first-class carriages to reduce overcrowding and improve energy efficiency.

Bernd Riexinger, the co-leader of Die Linke party, said having two classes of travel in regional trains in particular made no sense when the emphasis should be on energy efficiency and making rail travel more accessible.

“People are standing in the corridors, while in the first class there’s loads of free space,” he told the news network RND. “We are affording ourselves the luxury of dragging along almost empty first-class carriages in overcrowded express trains. All carriages should be open to everyone so that in one stroke we’d have more capacity – and almost without having to pay extra for it.”

Urging Deutsche Bahn to seriously consider his proposal, Riexinger added that people managed to travel without two classes of seats in buses.

Bernd Riexinger, co-leader of Die Linke. Photograph: John MacDougall/AFP/Getty Images

But the proposal was dismissed as “indecent nonsense” by Karl-Peter Naumann, head of the German passenger association, Bahn. Overcrowding on trains was due to too many first-class seats, he told the news agency DPA. “There’s a demand for first-class travel from commuters as well as those travelling longer distances. If I want to create more space, I simply need longer trains.”

The transport association for the Berlin-Brandenburg region, VBB, said surveys had shown that passengers were not in favour of scrapping first class. “Whenever a train has fewer first-class seats than planned, we immediately get customer complaints,” a spokesman said.

The German government’s rail ombudsman also waded into the row, dismissing Riexinger’s suggestion as “socialistic levelling”. Enak Ferlemann said: “If someone is prepared to pay more for broader seats and more room they should be allowed to enjoy their journey this way.”

The transport expert for the pro-business Free Democrats party, Torsten Herbst, told RND the proposal “to improve a form of transport by worsening” what was offered belonged “in the intellectual world of those who support the class struggle”.

Riexinger’s proposal follows a suggestion made last month by Luise Neubauer, of the environmental movement FridaysForFuture (FFF). She proposed a ban on domestic air travel in Germany, describing it as superfluous, and said people should be encourage to travel by train instead.

Since the rise of FFF, the topic of flugscham, or the shame of taking a flight, has entered mainstream discourse. Critics say the German rail system has been slow to develop. Its inefficiency and gaps in the network leaves many people with little choice but to fly on some routes, they say.

The completion in 2017 of an express line between Munich and Berlin, part of a “unity” project to join up east and west Germany, has cut the train journey time from over six hours to just under four. The journey between Berlin and Frankfurt is also now under four hours following improvements, effectively rendering air travel between the two obsolete, not least because both cities’ airports are far from their centres.

Nevertheless, increasing problems with delays and overcrowding on the rail network has drawn negative publicity for the Deutsch Bahn, a private joint-stock company whose sole shareholder is the state.