Kokh was elected on Feb. 26 by the Leningrad region's legislature to represent the region in the upper house.
Federation Council member Oleg Petrov has since filed suit in the Leningrad region city of Vyborg, asking that the election results be reviewed.
Kokh's nomination came as a surprise to a number of regional legislators. He was nominated shortly before the voting, effectively stalling the candidacy of Oleg Safonov, a security adviser to the regional governor who had been expected to take up the post.
Kokh received 29 votes to Safonov's 12. Four deputies voted against both candidates.
Petrov said the nominating procedure had been violated, declining to go into detail, Kommersant reported. The Vyborg court scheduled a review for Wednesday, the day the upper house is expected to confirm Kokh as a senator.
Leningrad region prosecutor Yury Prokofyev filed another case -- this one in St. Petersburg's Smolny district court -- asking that Kokh's election be annulled because the candidate declared his income improperly by submitting it in handwritten form.
Prokofyev also sent his complaint to the Leningrad legislature for review.
Federation Council Speaker Sergei Mironov told Kommersant that the upper house would consider the charges if it were to receive a formal complaint before next Wednesday.
As head of the State Property Committee in the 1990s, Kokh oversaw the so-called loans-for-shares program, widely reviled for selling major assets for tiny sums. Kokh was fired after the 1997 sale of the Svyazinvest telecoms holding.
He was appointed to head Gazprom's media arm in 2000 and played a large role in the takeover of NTV television.
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