Opponents of Angela Merkel are using the type of tactics that led to the rise of British Labour's Jeremy Corbyn to try to stop her forming a new government in Germany.
A rebel movement is urging thousands of people to become members of the centre-left Social Democrat Party (SPD) in order to block it joining a new coalition under Merkel.
The initiative is being spearheaded by the SPD's youth wing, the Jusos, which narrowly failed to stop the party entering formal coalition negotiations in a vote at the weekend.
A final deal still has to be approved by a full vote of the membership, and the Jusos activists believe they can recruit enough members to block it.
"For the next step, we need you NOW," Kevin Kuhnert, the Jusos' 28-year-old leader, tweeted alongside a link to apply for SPD membership.