Barnsley have accused Millwall of causing "unrest" after a potential change to the kick-off time of next month's Oakwell clash between the clubs was announced by the Lions.
Millwall on Tuesday published a statement on their official website regarding the March 17 fixture and the April 14 match against Sheffield United at Bramall Lane, each of which are scheduled to start at 3pm.
It said Millwall had been advised by South Yorkshire Police that they were looking to bring both kick-offs forward to 12.15pm.
The statement read: "The club has queried the reasoning and justification for this but until confirmation is announced supporters are urged against booking any transport."
Barnsley then put out a statement of their own on their website, which read: "We would like to apologise to our fans for finding out about a potential fixture change, through the away side.
"Barnsley Football Club would like to clarify a recent statement from Millwall Football Club.
"There has been a discussion regarding a potential change in kick-off time for the fixture against Millwall at Oakwell on March 17. The match is currently scheduled to kick-off at 3pm, but there has been a request from South Yorkshire police to change this to an earlier time.
"Barnsley Football Club will only release information when it is a fact. The release of this information prior to it becoming a fact has now created 'speculation' and caused unrest amongst fans.
"This information was released without any prior contact to Barnsley Football Club from Millwall and we can only apologise for this being released.
"We will of course update fans as a priority when this issue has been finalised."