The letter, co-ordinated by Labour MPs Jess Phillips and Stella Creasy and signed by cross-party members and peers, reads: "We do not presume guilt, of course, but we believe due process should be followed and the [Swedish] complainant should see justice be done".
Assange first sought asylum in the Ecuadorian embassy in 2012, when he skipped bail after an extradition order to Sweden, where someone had accused him of sexual assault.
Swedish prosecutors dropped a rape investigation into Assange in 2017 because they were unable to formally notify him of the allegations - a necessary step in proceeding with the case - while he remained in the Ecuadorian embassy.
The letter was copied to Diane Abbott, Labour's home affairs spokeswoman, who has separately cautioned that agreeing to the United States extradition request "would be wrong" because Assange was acting as a whistleblower.
A witness who prosecutors were seeking to interview and an associate of Assange based in Europe who also requested anonymity said that before his arrest Assange had expressed concern that USA prosecutors would also bring charges against him related to WikiLeaks' publication of Central Intelligence Agency computer hacking tools, which the website described as its "Vault 7" cache.
Assange is due to face a hearing over his possible extradition to the United States on May 2.
The official, who wished to remain anonymous, says U.S. authorities have already sent Britain a provisional arrest warrant regarding Assange's extradition.
She said they had not received any prior notice of it and called on Swedish authorities to reopen the case.
Magic Johnson abruptly resigns as Lakers president
He said he was exhausted of not being able to talk to players on other teams and mentor them without the specter of tampering. They haven't made the playoffs since 2013. "The Lakers will have an opportunity to get Kyrie Irving to come to L.A".
"Regardless of where you stand on this, he must face these allegations in Sweden and clear his name if he thinks he's innocent", Maajid said.
If Britain receives competing extradition requests, lawyers say the Home Secretary would have some leeway in deciding which takes priority.
His fears abruptly turned into reality on Thursday after Ecuador withdraw its asylum and he was charged and promptly found guilty of breaching bail in Westminster Magistrates Court by judge Michael Snow, after originally failing to surrender to the court in 2012.
Assange denies both allegations.
Sweden's Prosecution Authority said Thursday they were considering reopening the investigation against Assange.
She said she was "disgusted" the American allegation had been "allowed to eclipse" the sex offence case.
The 47-year-old's Swedish lawyer, Per E Samuelson, told local media it would be "highly unlikely" Assange would face a Swedish courtroom, and that the US's extradition request would trump Sweden's.
Julian Assange's unceremonious removal from the Ecuadorian embassy in London makes headlines on Friday, along with Brexit and the Duchess of Sussex.