The Parramatta Eels are investigating the systematic tampering of memberships in the lead-up to last year's Parramatta Leagues Club elections and a break-in and suspected theft of their records.

While Brad Arthur's rejuvenated team are sitting fourth on the NRL premiership ladder after 11 rounds, the fresh off-field probe has found up to 150 memberships were covertly entered into their database and backdated by three years in a ploy that gave those members automatic voting rights.

The tampering is alleged to have been carried out on club computers on April 4 and April 5, 2013, mostly between 6am and 9am when the Parramatta Leagues Club was not open.

And in a further development, the Eels have called in police after a break-in and the alleged theft of records last week from their archives facility near the club headquarters. Furthermore, witnesses have told officials there was an attempt to break into a private audit room that has been set up inside the leagues club building to carry out the investigation.

The internal inquiry, still in its early stages, continues with an investigator to be added to the team of six IT personnel who have been trawling through the club's electronic records for several weeks.

Parramatta Leagues Club (PLC) chief executive Bevan Paul on Tuesday confirmed the Eels' new inquiry and its alarming initial findings when contacted by the Herald.

''What we know is that there has been some tampering of membership records and the tampering is of a nature that would suggest the objective is so those people could vote,'' Paul said.

The backdating of new memberships occurred just weeks before last year's PLC elections on May 11 and is alleged to have begun three days after Parramatta were thrashed 50-0 by the Roosters.

Members must be financial for three years and be board approved to vote, according to the Eels' constitution.

The poll of members was a tightly contested affair and produced a change of leadership, with Roy Spagnolo's Parra 4 Eva campaign unsuccessful in retaining the chairmanship he had held since 2009 and losing his place on the board completely.

TheHerald can reveal that many of the approximately 150 member records so far found to have been tampered with were in the names of associates, family or friends of Spagnolo. Of the memberships entered in a frenzied two days on the database last April and backdated so their registration dates read March 2010, six have the surname Spagnolo.

Among others to have had tampered memberships identified are Spagnolo's friend Roy Mittiga and six others with that surname, Spagnolo's brother-in-law Patrick Agostino, real estate agent Pat Sergi and three other Sergis, relatives of Spagnolo's friends George Gaitanos and Vince Lombardo, another Spagnolo business associate Chris Crawley and porn king Con Ange.

Sergi, named at the Woodward royal commission in relation to connections with former crime boss Robert Trimbole, last month appeared before the Independent Commission Against Corruption hearing into political fund-raising.

Three others identified as having memberships altered are Libertinis. Mario Libertini ran on Spagnolo's ticket at the 2013 election and is a PLC director. Spagnolo is still chair of the Parramatta District Rugby League Club, but was last October banned for two years from holding a PLC directorship.

Eels memberships are created and entered at the leagues club, with the new member's photo for their card taken by staff at the front desk before a generic backdrop.

Aside from the backdating, the Parramatta investigation found photographs on membership records with a different background, as well as some duplicates - photos that have been used for more than one membership. It is understood that a few of the members were listed as being 18 years of age, meaning they would have been only 15 - three years below the age of eligibility - when they supposedly first became financial members.

Paul said the inquiry had not yet determined who was responsible for the tampering, but confirmed the changes occurred mostly early on two mornings in April during hours when the leagues club was closed.

''The records suggest that, yes,'' Paul said. ''Some has been; we don't know if all of it has been because we haven't finished looking at all the records yet.''

He said it was suspected records had been taken from the club's archive facility on Ferris Street during a break-in last week.

''We think so, yes,'' Paul said. ''But we don't have an inventory of what was stored down there, so it's hard to say what was stolen.''

The Eels are already awaiting the outcome of a NSW Office of Liquor Gaming and Racing Investigation into alleged irregularities under the previous administration, and Paul is expected to update PLC directors on the findings of the new probe at a board meeting on Friday morning.

Spagnolo did not return the Herald's calls on Tuesday.

Do you know more? chris.barrett@fairfaxmedia.com.au

Twitter - @ChrisBarrett_