"I recommend them to remain in their seat so that no one else can replace them," said Stig-Erik Werner, a former Sweden Democrat now independent councillor in Tidaholms municipality, to the Expressen daily.
Werner was kicked out of the Sweden Democrats in September and is one of the administrators of a group calling themselves "Nationalkåren" (literally: national corps), a network of former Sweden Democrats formed to oppose the party.
"Go for it William Petzäll!!! If you want you are welcome in the National Corps," Werner wrote on Petzäll's Facebook page shortly after his decision was reported by Expressen on Monday.
On Wednesday morning William Petzäll was listed as a member on the group's Facebook page.
"Nationalkåren", a self-proclaimed nationalist organisation, now lists several former Sweden Democrats among its membership and actively seeks contact with others who have been excluded from the party for various reasons.
Werner explained to the newspaper that the purpose of the group is to encourage ex-Sweden Democrats to remain in their elected positions and thus block the party from appointing more "obedient" members as replacements.
William Petzäll announced on Monday that he had decided to leave the party and remain in the Riksdag as an independent.
The 23-year-old explained his decision that he plans to use his seat in the Riksdag to "push my pet issue and increase awareness. To develop more concrete measures to help young alcoholics and drug addicts."
Petzäll was forced to take time out from politics in February after he turned up at a party in Trelleborg drunk and disorderly, later spending the night in a police jail cell to sober up.
After failing to adhere to a drug and alcohol rehabilitation programme the party hierarchy called on Petzäll to resign his seat and step aside. The young MP refused.
According to senior party member Erik Almqvist, Petzäll demanded up to 3 million kronor from the party as his price for vacating his seat. A demand that the party refused to agree to.
In an interview with the Nyheter 24 news website on Tuesday, Petzäll rejected the claim and responded by threatening to reveal party secrets if the "smear campaign" against him continued.
While Petzäll is the first of the 20 Sweden Democrat MPs to leave the party, he is the latest of a series of high-profile departures from the party since the 2010 election.
Many of the ejected party members have elected to remain in their positions at municipal and county councils across Sweden, refusing to adhere to party demands to step aside.
Among the more notable dissenters are Thomas Karlsen who was group leader for SD in Trollhättan in western Sweden and was kicked out of the party after comments on social media referring to the July terror attacks in Norway.
Further high profile rebels include David Kronlid in Örebro, Olle Larsson in Härjedalen and Mikael Säbom in Strömsund.
SD press secretary Eric Myrin in August called on all the SD rebels to vacate their seats and on Monday the party issued a statement calling on Petzäll to "take his responsibility" and do the same.
"The Sweden Democrats regret that William Petzäll is now choosing to remain in the Riksdag without party affiliation. We continue to hope that he will take his responsibility to himself and the party's voters," a statement from the party on Monday read.