Leeds fans have complained to police about alleged offensive chanting by Millwall supporters during a Championship match at the London club's ground.
Leeds United Supporters Trust (LUST) said Millwall fans sang songs before kick-off mocking the killing of two Leeds fans in Istanbul, Turkey.
The group said it will complain about "inaction" by officers and stewards inside the ground to halt the chanting which took place at The Den, Millwall's stadium in Bermondsey.
Millwall FC told IBTimes UK an investigation will be conducted when a complaint from Leeds fans has been received.
A LUST spokesman claimed the alleged chanting breached Public Order laws, saying: "Before kick-off, a section of the home crowd began chanting about the deaths of two Leeds United fans in Istanbul, Turkey.
"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.
"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," said a statement.
Christopher Loftus and Kevin Speight were stabbed during street clashes in Istanbul in April 2000, the night before Leeds and Galatasaray played a Uefa Cup semi-final. Their killer was jailed for 15 years.
According to eye-witnesses, a section of Millwall fans chanted 'Istanbul' repeatedly in a reference to the deaths. On-lookers also heard the chant 'Always look out for Turks carrying knives' sung to the tune of Monty Python's 'Always look on the bright side of life.'
One fan who was at the game said he heard chanting. He told IBTimes UK: "It's not right. But the Leeds fans were chanting about the 1958 Munich air disaster. Two wrongs don't make a right."
A Millwall spokesman said the club had a good relationship with Leeds FC. "As and when we received a complaint from Leeds we will investigate it. We have CCTV, but it should first and foremost be referred to police."
A Metropolitan Police spokesman said: "There were no complaints made about chanting to the police during the course of the match. One Millwall fan was arrested for making gestures. When the club has received complaints it has always been pro-active in responding to them."