LUST claims Millwall supporters were taunting the visitors about the death of two Leeds fans in Istanbul in 2000 before and during Saturday's game, which Millwall won 2-0.
"Before kick-off, a section of the home crowd began chanting about the deaths of two Leeds United fans in Istanbul, Turkey," read a LUST statement.
"This was in full view of many stewards of Millwall Football Club and the Metropolitan Police. These chants are totally unacceptable and, in our opinion, caused alarm and distress to the Leeds fans within the ground.
"It is our opinion that offences under section five of the Public Order Act 1986 were being committed and ignored by officers of the Metropolitan Police.
"As a result of the inaction from stewards of Millwall Football Club and officers from the Metropolitan Police further chanting of a similar nature continued with other sections of the home support joining in, especially throughout the latter stages of the game where they were widespread throughout the ground.
"The Leeds United Supporters Trust will be taking strong action in the form of official complaints to both Millwall Football Club and the Metropolitan Police."
Leeds fans Christopher Loftus and Kevin Speight both died after being stabbed during street clashes the night before Leeds played Galatasaray in a UEFA Cup semi-final in April 2000.