BERLIN, Feb. 21 (Xinhua) -- The youth organization (Juso) of the German Social Democrat (SPD) has urged the party leadership to formulate a "plan B" to joining another grand coalition on Wednesday.

Many SPD members were openly wondering "whether the SPD would be able to remain functional after a no vote (in ongoing referendum)", Juso leader Kevin Kuehnert told press in Berlin.

Kuehnert's comments were made only a day after a membership poll was opened to determine whether the SPD should form a new government with the Christian Democratic Union (CDU) and Christian Social Union (CSU). 463,000 party members are eligible to cast their vote, the results of which are scheduled to be announced by the SPD leadership on March 4.

The referendum is widely seen as the final hurdle to be taken by German Chancellor Angela Merkel (CDU) as she seeks to form what would be her fourth governing cabinet.

German has been without a designated federal government since national elections in September, plunging the Europe's largest economy into an unfamiliar state of political uncertainty.

Whether an arduous process of coalition negotiations ultimately proves successful for Merkel is still unclear, as significant factions in the SPD have sought to persuade members to oppose the final agreement secured by ex-party leader Martin Schulz with the leaders of the CDU and CSU.

Juso-chief Kuehnert in particular has voiced fears that another term as junior-partner under Merkel could lead to the electoral marginalization of the SPD.

A recent poll of voter support showed that the party had slumped to a historical low of 15.5 percent, languishing behind the CDU as well as the far-right Alternative for Germany (AfD).

Ignoring Kuehnert's calls to think seriously about an alternative to participation in the federal government, however, SPD parliamentary faction leader Andrea Nahles has called on the party membership to vote in favor of another "grand coalition."

Highlighting the significant concessions from the CDU on Europe, wages and pensions achieved in negotiations, Nahles urged SPD politicians to demonstrate more discipline and refrain from internal quarrelling in response to poor polling results.

"The SPD is in a very serious situation", Nahles told the "Redaktionsnetzwerk Deutschland" (RND).

Speaking to the newspaper "Frankfurter Allgemeine Zeitung", Stephan Weil (SPD), governor of Lower Saxony, echoed Nahles' concern that his party was experiencing a period of intense difficulty.

Nevertheless, Weil expressed optimism that the "necessary steps have just been taken to start a come-back." In Weil's view, the SPD was merely experiencing a temporary set-back because it had finally committed to clear positions on refugee policy and public expenses.

In a similar vein, SPD parliamentary secretary Carsten Schneider, told press that there was no Plan B to the grand-coalition. "I firmly anticipate that it will work and don't have another plan", Schneider said.

If Schneider's confident forecast for the SPD referendum proves true, Merkel could formally be re-inaugurated as Chancellor by March 14.