Police are investigating racist emails and letters sent to Peterborough's MP Fiona Onasanya when she was jailed.
The independent MP has now been released from prison after serving a month of her sentence for perverting the course of justice.
The 35 year old was expelled from the Labour Party following her conviction for lying about a speeding ticket. She remains an MP.
It has now emerged police in Cambridgeshire and South Yorkshire are investigating "reports of malicious communications" sent on January 29.
In a statement, Ms Onasanya's communications officer Matt Turner said: "Many of these emails and letters have a disgusting racial element to them.
"This despicable and threatening behaviour is unacceptable and we welcome an investigation."
Ms Onasanya, a solicitor, still received her £77,379 salary while in jail despite missing votes in the Commons.
She can return to Parliament to take part in crucial Brexit votes after being released from prison.
Having been freed under an early release scheme, it is almost certain the Remainer will be wearing an electronic tag as part of strict conditions if she attends Wednesday's Commons debates and votes.