Cardiff council said officers were following "clear instructions" to "maintain neutrality".
Plaid Cymru candidate Neil McEvoy said that Cardiff council had been removing his placards from outside homes in Cardiff West, where he is standing.
He said the council had "no right" to remove the boards.
Mr McEvoy, who is also a candidate in South Wales Central, claims that some of the placards were taken from private property.
In a statement, passed to Mr McEvoy by the police, the council said: "To maintain neutrality during the pre-election period and in line with guidance to the local authority, caretaking services officers are following clear instructions to remove all political posters, irrespective of party or candidate from communal areas in council properties.
"This includes garden areas in flats, or inside blocks but not individual gardens, regardless of whether it is a council property or not."
South Wales Police told Mr McEvoy that it had recorded a complaint about theft of and damage to Plaid boards. A police inspector said "that is still under investigation".
But he told Mr McEvoy that he did not intend "to record any additional complaints of theft as a result of any disputes over ground ownership".
"I believe as a local councillor it is proportionate and reasonable for you to address this with your peers and resolve within your own organisation," he added.
A local authority has admitted removing political posters from communal areas around council homes.