The National Crime Agency (NCA) confirmed it had acted on information passed on by the Sun on Sunday newspaper.
The tabloid reported an undercover investigator met Sodje, who allegedly said he could arrange for footballers in the Championship to get themselves a yellow card in return for tens of thousands of pounds.
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Sam Sodje said he arranged for players to get booked in exchange for thousands of pounds
The 34-year-old also claimed he could rig Barclays Premier League games and even said he was preparing to fix matches at next year's World Cup in Brazil, the newspaper reported.
Portsmouth FC spokesman Colin Farmery said: "If these serious allegations are true then we are extremely shocked and saddened by them, as match-fixing of any type goes to the heart of the integrity of the game.
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Sodje is at the centre of a new match-fixing scandal
"The player in question no longer plays for the club and we have not been contacted by the authorities, but of course we would cooperate fully with any inquiry."
It was also reported Oldham Athletic player Cristian Montaño failed to get a yellow card in return for money in a match against Wolverhampton Wanderers on October 22 and offered to take part in another rigging incident.
Oldham said in a statement: "Oldham Athletic Football Club has been made aware of the incident and allegation surrounding one of its players, Cristian Montaño. The club will commence an immediate internal investigation to establish all the relevant facts of the case.
Match-fixing controversies
Soccer - FA Carling Premiership - West Ham United v Crystal Palace (01 of08)
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In February 1999, a Malaysian-based betting syndicate was caught attempting to install a remote-control device to sabotage the floodlights at Charlton Athletic's ground with the aid of a corrupt security officer. If the match had been abandoned after half-time, the result and bets would have stood... (credit:PA)
Selhurst Park/floodlights failure(02 of08)
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Subsequent investigations revealed the same gang had been responsible for previously unsuspected "floodlight failures" at West Ham's ground in November 1997 and a month later during Wimbledon's match with Arsenal at Selhurst Park. (credit:PA)
Former South African cricket captain Hansie Cronje(03 of08)
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CAPE TOWN, SOUTH AFRICA - JUNE 15: Former South African cricket captain Hansie Cronje raises his hand to take the oath prior to testifying before the King Commission of Inquiry into allegations of cricket match-fixing in Cape Town 15 June 2000. Cronje confessed to pocketing large sums of money during a five-year flirtation with bookmakers and vowed that he would not play representative cricket again as punishment. (Photo credit should read ANNA ZIEMINSKI/AFP/Getty Images) (credit:Getty Images)
Hoyzer Sentenced to Two Years(04 of08)
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BERLIN - NOVEMBER 17: Former German soccer referee Robert Hoyzer leaves court after receiving a two-year and five-month sentence November 17, 2005 on the tenth and final day of hearings in Berlin, Germany. Hoyzer took payments from a Croatian-led betting ring to manipulate four soccer matches in one of Germany's worst-ever soccer scandals. (Photo by Sean Gallup/Bongarts/Getty Images) (credit:Getty Images)
Juventus' general director Luciano Moggi(05 of08)
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Bari, ITALY: Juventus' general director Luciano Moggi phones as he leaves the San Nicola stadium in Bari after the Italian serie A football match Reggina vs Juventus, 14 May 2006. Luciano Moggi resigned after Juventus claimed their 29th Serie A title with a 2-0 win away to Reggina on the final day of the season. (credit:Getty Images)
(06 of08)
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In July 2007 it was revealed NBA referee Tim Donaghy had gambled on 10 to 15 games, including games which he officiated. Donaghy was sentenced to 15 months in federal prison. (credit:Getty Images)
Spot-fixing, 2010(07 of08)
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Undercover reporters from News of the World secretly videotaped Mazhar Majeed accepting money and informing the reporters that fast bowlers Mohammad Asif and Mohammad Amir would deliberately bowl no balls at specific points in England's innings.The no balls were duly bowled at the exact stages predicted, and the International Cricket Council (ICC) banned Asif, Amir and Salman Butt for terms of between five and 10 years.In November 2011, Butt and Asif were found guilty by a London court on criminal charges relating to spot-fixing. Amir and Majeed had entered guilty pleas on the same charges. All four were given prison sentences, ranging from six months to 32 months.
Snooker - Stephen Lee Filer(08 of08)
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Stephen Lee was banned for 12 years after being found guilty of seven match-fixing charges earlier this year. (credit:PA)
"The club is co-operating with other agencies in this matter and cannot comment on specific facts at this stage. The club will not be issuing any further statements at this time."
An NCA spokeswoman said: "An active NCA investigation is now under way and we are working closely with the Football Association and the Gambling Commission.
"Six people are in custody and are being questioned by NCA officers. We cannot comment further at this stage."
Michael Boateng and Hakeem Adelakun, both 22, were charged last week with conspiracy to defraud contrary to common law.
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Montaño (left) has also been drawn into the scandal
The pair, who played for Conference South club Whitehawk FC in Brighton, were dismissed by their club and will appear in court on Wednesday.
Two other men, Chann Sankaran, 33, from Hastings, East Sussex, and Krishna Sanjey Ganeshan, 43, from Singapore, were charged last month with plotting to defraud bookmakers and will also appear in court this week.