Around 7,000 candidates have registered to stand in the 12 May poll, with 329 parliamentary seats up for grabs.
As the clock struck midnight on Friday, volunteer workers spread across the country to put up posters of the candidates, AFP
"At midnight sharp, they began pulling down pictures of the martyrs and replaced them with posters of the thieves," said Baghdad resident Settar Tourki.
Martyrs refer to the thousands of government forces and allied militiamen killed fighting to push back the Islamic State
after the group launched a sweeping offensive in 2014.
Pictures of these forces killed in combat dot the streets of Baghdad and major cities and towns.
Social media users cried foul as pictures of politicians, referred to by some in Iraq as "thieves" over allegations of corruption
, replaced those of combatants.
Facebook user Laith al-Shommari denounced what he called an "insult" to the memory of fighters "who have sacrificed their lives so that we can live in peace and security".
"We should burn the electoral posters of all these cowards and opportunists," he said referring to the candidates.
The May elections will be the fourth parliamentary and provincial assembly polls since the ouster of dictator Saddam Hussein in a US-led invasion
Iraqi elections have generally been free since the US invasion, but politics have been dysfunctional because of the tremendously sectarian nature of the vote and of the major parties, such that the results are more like a census than a contest of ideas.
This time around Iraq's Sunni Muslims, hundreds of thousands of them internally displaced after the destruction of their towns during the war, have grown increasingly angry as they struggle, mostly without help from the government.
Meanwhile, Iranian-backed Shia militias, who played a key role in defeating IS and are allied with the Shia-led Baghdad government, are poised to make significant electoral gains.
Many candidates appear to be trying to distance themselves from openly sectarian rhetoric in the run-up to the vote, saying they have worked to form diverse, non-sectarian coalitions.
The post-election creation of a parliament majority, however, is expected to be sectarian in nature.