Matvienko

Ms. Matvienko, who declined to comment for this article, has said her entrance to the race was legal.

St. Petersburg Scandal: A 'Secret' Election Alan Cullison 2011

The Kremlin-dominated upper house is prepared to call a special session to elect Ms. Matvienko speaker before the legislature formally reconvenes Sept. 21, the government-run RIA Novosti news agency reported, citing Vice Speaker Svetlana Orlova.

St. Petersburg Scandal: A 'Secret' Election Alan Cullison 2011

Kremlin critics in St. Petersburg are going door to door in both districts urging residents to vote for anyone but Ms. Matvienko, mainly to sound a protest.

St. Petersburg Scandal: A 'Secret' Election Alan Cullison 2011

Ms. Matvienko is expected to win easily in at least one of Sunday's races.

St. Petersburg Scandal: A 'Secret' Election Alan Cullison 2011

In June, just 18% rated Ms. Matvienko positively in a poll of 500 St. Petersburg residents by the independent Levada Center.

St. Petersburg Scandal: A 'Secret' Election Alan Cullison 2011

But in late July, Ms. Matvienko dropped a bombshell: In a television interview she said she had registered in two other districts.

St. Petersburg Scandal: A 'Secret' Election Alan Cullison 2011

A victory Sunday would make Ms. Matvienko eligible for a presidential appointment to the Federation Council, the upper house of parliament.

St. Petersburg Scandal: A 'Secret' Election Alan Cullison 2011

But Natalya Petukhova, an official with the opposition party Just Russia, said Ms. Matvienko made opposition difficult because she refused to say in which district she would run.

St. Petersburg Scandal: A 'Secret' Election Alan Cullison 2011

After years of intense protests, Ms. Matvienko agreed late last year to move the tower outside the city.

St. Petersburg Scandal: A 'Secret' Election Alan Cullison 2011

This year it became clear the Kremlin may need to replace Ms. Matvienko to boost its local ratings.

St. Petersburg Scandal: A 'Secret' Election Alan Cullison 2011