Steenkamp, a law graduate and former FHM cover star who had been dating the Olympic and Paralympic athlete for a few months, died in a shooting at Pistorius's Pretoria home in the early hours of Thursday (February 14). Pistorius arrived at court on Friday morning to face a charge of murder.
Directly addressing The Sun's owner and News Corporation founder Rupert Murdoch on Twitter, Lord Prescott wrote: "A new low for your paper The Sun. Do you really think this [cover] is appropriate?"
The cover features a large image of Steenkamp wearing a pink bikini, along with two smaller pictures of Pistorius - one showing him leaving a police station on Thursday and a second of the sprinter on track.
Lord Prescott - a former Labour Deputy Prime Minister - also posted the telephone number of The Sun and editor Dominic Mohan's work email address on his Twitter feed, accompanied by the hashtag #HerNameWasReevaSteenkamp.
"So [East Guildford Liberal Democrat council candidate] @georgewpotter phoned Sun Newsdesk to complain," Lord Prescott later wrote. "They say, 'She was a model so it's just a photo of her working'."
He also claimed that the newspaper had paid "up to £35,000 for that picture on the front page", and added: "I really hope every member of the Shadow Cabinet thinks twice before writing for The Sun after that front page."
A petition has also been launched on change.org, in which the petition creators describe the cover and choice of image as "distasteful" and "disrespectful".
The petition also calls on The Sun to apologise and accuses the paper of "objectification" of Steenkamp after her death.
Oscar Pistorius career in pictures:
Copyright: PA Images