Voters in over a dozen Russian regions and cities, including St. Petersburg, will head to the polls in September to elect their executive and legislative representatives. Observers have pointed to a number of obstacles preventing the opposition from registering as candidates in Russia’s second-largest city months ahead of the vote.

Opposition politicians are facing mounting challenges from officials in St. Petersburg in getting on the ballot ahead of local elections this fall, Russian media outlets have reported.

One St. Petersburg district alone had denied registration to more than 10 members of three major opposition parties, the Yabloko opposition party told the Znak.com news website on Wednesday.

Yabloko's nominee for governor, Boris Vishnevsky, was also barred from getting on the ballot after failing to collect the required number of signatures from municipal deputies, most of which hail from the ruling United Russia party.

Meanwhile, the social-democratic Just Russia party said none of its members had been allowed to register as candidates for municipal seats in a different St. Petersburg district. Officials reportedly told them they had failed to submit the required documents.

Claims of violations have led Russia’s top election official to threaten to cancel St. Petersburg’s local race altogether. Her colleagues later appeared to walk back from the warning.