Whether previous non-voters go to the polls could be the decisive factor in the upcoming federal parliament elections in Germany, according to opinion poll results published by German newspaper "Bild" on Monday.

Every fifth person who is planning to support the center-left Social Democrats (SPD) in the upcoming election did not vote in 2013, according to "Bild." In contrast, only every 10th person planning to cast a ballot for the conservative Christian Democrats (CDU) or Bavarian sister party Christian Social Union (CSU) stayed away from polling stations in the last election.

This comes amid an overall surge for the SPD following the announcement that former EU President Martin Schulz would be their choice of candidate to run for chancellor. Schulz will face off against sitting chancellor Angela Merkel, who is running for the CDU/CSU bloc. 

Merkel, once uncontested as Germany's most popular politician, has recently struggled against criticism over her refugee policy, including from her own party.

Best SPD results in years

Another poll published by "Bild" on Sunday predicted that the SPD would receive 32 percent in the September election, while the CDU/CSU would get 33 percent; the best ratings the Social Democrats have received against the conservatives in years.

"Since Martin Schulz announced his candidacy for the chancellorship, the number of people who did not vote in 2013 and are now planning to vote for the SPD has risen by roughly 70 percent in the last 14 days," Bild wrote on Monday. The number of previous non-voters planning to support the CDU/CSU has fallen by 30 percent.

The nationalist Alternative for Germany (AfD) - which brought the most non-voters to the polls in several state elections last year - also lost support dramatically. Forty percent fewer former non-voters expressed their support for the party.

Coalition likely

Up to six parties are expected to make it into the German federal parliament in the September election. If no party receives an outright majority - an outcome widely seen as likely - two or more parties will have to form a coalition government.

As the two largest parties, the SPD and the CDU/CSU have both staked their claim to run the next German government. They are expected to campaign against each other, even though they are currently running the German federal administration together in a so-called "grand coalition."

Four other parties are currently polling above 5 percent, the threshold parties need to meet in order to make it into the parliament. According to "Bild," the AfD is expected to garner 10 percent of all votes, the Left party 8 percent, the Greens 7 percent, and the pro-business FDP 6 percent.