The woman, who is not being named, was suspended on Friday with immediate effect while the potential clash of interests is investigated. She alerted the OPLC of the situation on Thursday night.
The OPLC board, in charge of securing the future of the Olympic Park site, voted 14-0 in February to make the Hammers the first choice to move into the £486million stadium. The Hammers were in a head-to-head contest with Tottenham.
A statement from the OPLC read: "It has come to our attention that an employee of the Olympic Park Legacy Company has been undertaking paid consultancy work for West Ham United FC.
"The company had no knowledge of this work and no permission was given to undertake it. This individual had no involvement whatsoever in our stadium process.
"The individual concerned had declared a personal relationship with an employee of West Ham United FC when she joined the organisation and we therefore put robust measures in place to ensure our stadium process was not compromised.
"The stadium team has been based at our law firm Eversheds' offices in the City and only the stadium team had access to information about the bids.
"As soon as this new information came to light, the company took immediate action and launched an independent investigation.
"The employee has been suspended pending the outcome of this."
The discovery about the employee's work status came to light on Friday.
West Ham also released a statement, stressing their belief that the bidding process had not been compromised.
The statement read: "We have become aware of enquiries being made in respect of a lady who has undertaken work for West Ham United on a consultancy basis relating to the Olympic Stadium project.
"Having learned of the enquiries, we have undertaken an initial internal investigation.
"We have established that the work that was carried out was not connected in any way to the bidding process for the Olympic Stadium, but procurement project management thereafter.
"We are of the firm view that the integrity of the bidding process has not been compromised.
"We consider that the bidding process was robust and believe that remains the case."
The woman, who has been suspended on full pay, told her bosses at the OPLC that she was in a relationship with a West Ham employee when she got the job at the company.
The OPLC stressed they did not know about any other connections with the east London club until Friday.
It claimed it had been "meticulous" and taken care to be "robust" about the bid process due to the sensitivity of the hotly-contested campaigns to move into the Olympic Stadium.
The decision to award the Olympic Stadium to West Ham is still subject to possible High Court legal judicial reviews.
The OPLC moved the base for the Olympic Stadium bidding process away from their east London headquarters to their lawyer's offices in central London.
It is believed that this precaution has given the OPLC confidence that no information could be discovered, even accidentally.
This week Tottenham went back to the High Court to continue their bid for a judicial review of the decision to award the Olympic Stadium to West Ham.
Spurs are refusing to accept defeat after last week's decision by Judge Mr Justice Davis to reject their bid and that of Leyton Orient's.
The north London club will now have the chance to make a case in an oral hearing at the High Court.