"This is not the first time the Socialists help Germany take over Europe", say the new ads in the Stockholm underground, which is part of the right-wing Sweden Democrats EU election campaign.
The posters also feature the German flag used in Hitler's first few years in power alongside the swastika flag.
The Sweden Democrats (SD) explained their campaign was meant to highlight the hypocrisy of the Social Democrats, their nemesis, who often accuse others of Nazism.
"To Nazi stamp their political opponents is for the Social Democrats a common method of campaigning. It doesn't really matter if you are liberal, right-wing, conservative, or anything else they don't like — for the Social Democrats are still a potential Nazi", the Sweden Democrats explained.
"This is despite the fact that the Social Democrats are the party that most helped Nazi Germany during WWII. They lent train wagons, provided the German Armed Forces with steel, allowed German troop transports through the country, etc. It was the Social Democrats who demanded that Hitler's Germany should stamp Jews' passports with J in order to reject Jews at the border. The Social Democratic government also censored Swedish media that tried to report on the Nazi torture and concentration camps", the Sweden Democrats explained.
"Today, the Social Democrats are still chanting anti-Semitic songs on streets and squares. In an attempt to censor the media once, the Social Democrats are once again helping the great powers of Europe, with Germany at the forefront, to build an empire", the anti-EU party continued, alluding to a recent scandal surrounding the Social Democrats' youth wing.
According to SD communications manager Joakim Wallerstein, the Social Democrats put themselves into this position by repeatedly raising Nazism in every election movement and attempting to paint their rivals as Nazis.
"So far, the reactions have been very positive. <…> The most common comment is that people think it is good to lift this up because the Social Democrats brown-stamp virtually all other parties", Wallerstein told the news outlet Nyheter Idag.
"If you read about Adolf Hitler's politics and methods, you see many scary similarities with Stefan Löfven and his Social Democrats", a user ventured on Facebook.
"Not to mention forced sterilisation and lobotomy. The Nazis ended it in 1945 when the war ended, but Socialists continued until 1975. History is written by the winner, but the truth always comes forth", another user pointed out.
Others, by contrast, argued that SD's rummaging in the past was useless and harmful.
The Social Democrats themselves, retorted by accusing the SD of Nazism, once again playing the Nazi card.
"SD is now falsifying history the spirit of Goebbels", Justice and Migration Minister Morgan Johansson tweeted.
Prior to the 2018 elections, SD released the documentary film "One People, One Party", which also highlighted the Social Democrats' connections to Hitler's Germany.
Led by Social Democrats, who remained in power for the most part of the 20th century, Sweden assisted the Nazis during World War II. After the start of WWII, Sweden was the only major supplier of iron ore to the German war machine, while remaining formally neutral. In Sweden, there were even German-owned mines. However, recalling Sweden's war history remains a controversial topic.