A panel for the Parliamentary Assembly of the Council of Europe called on FIFA to examine whether Blatter — re-elected to a fourth, four-year term last June — abused his position ahead of the vote.
FIFA should probe "whether the candidates in its recent election for president — and particularly the successful candidate — exploited their institutional positions to obtain 'unfair advantages for themselves or for potential voters,'" the panel said.
Though he was facing criticism for alleged corruption in soccer's governing body, Blatter ran unopposed in 2011 when rival candidate Mohamed bin Hammam withdrew after being accused of bribing voters. Bin Hammam claims that Blatter helped orchestrate the bribery scandal, and is challenging his life ban by FIFA at the Court of Arbitration for Sport next month.
FIFA responded Wednesday that it already investigated the allegations against Blatter — and they were dismissed.
The new report also tried to increase pressure on FIFA to reveal details of a scandal involving its former marketing agency, which collapsed into bankruptcy in 2001.
FIFA should "publish in full any judicial and other documents" it has concerning the ISL case, in which senior soccer officials allegedly took millions of dollars in kickbacks from World Cup broadcast deals, the report said.
Blatter promised to publish a court dossier last year as part of a wide-ranging reform program. At least one party has appealed to Switzerland's supreme court to block publication of the material. FIFA said it "already stated its full support" for releasing court papers.
The BBC has reported that two Brazilian officials — Blatter's predecessor, Joao Havelange, and Ricardo Teixeira, a FIFA executive committee member who leads the 2014 World Cup local organizing committee — pocketed payments.
The Council's report pointed to Bin Hammam's case and a 2006 match-fixing scandal known as Calciopoli — which exposed Italian officials who selected referees to favour some clubs — as examples of how power struggles and economic interests "seriously jeopardized" ethics in sports.
"Moreover, the sports scandals that come to light are only the tip of the iceberg: experts are fully aware that the hidden part, unknown to the public, is even bigger and of a more worrying dimension," the report said.
The panel consulted FIFA officials before drafting the 20-page report.
Other proposals included limiting sports leaders to eight-year terms in office, requiring their salaries and bonuses to be published, and inviting "former athletes of acknowledged integrity" to serve on federation committees.
FIFA said the Council also praised "several positive elements" of its work, including its rules restricting international transfers of players under 18 and investment in social programs.
The report will be debated on April 25 when parliamentarians from 47 Council of Europe member states meet in Strasbourg, France.