Salford and Hull KR have issued statements to supporters ahead of their meeting at the AJ Bell Stadium this evening.
The Red Devils are jostling for position in the top five, while the Robins must win to guarantee Super League rugby for 2020.
And both clubs have moved to remind supporters of the expected standards of behaviour.
There were ugly scenes after full-time when the two sides met in the Million Pound Game two years ago, as supporters from both sides brawled on the field.
In a statement, Salford said: “Emotions are set to be high for the final match of the regular season and the Red Devils are encouraging all supporters to get behind their team in the correct manner.
“Supporters are invited to attend tonight’s fixture in fancy dress, as a celebration of a thrilling season across the division.
“A significant number of away fans are expected to travel, in support of Hull Kingston Rovers.
“We hope that the drama on the field provides excitement for both sets of supporters and they are able to cheer on their teams together.”
Hull KR said: “All fans are reminded to respect match officials, players and fellow spectators before, during and after the 80-minute contest.
“Though emotions promise to be high at the AJ Bell Stadium, Hull KR are appealing to the Red Army to support the team in the right way.
“During the 2019 campaign, isolated incidents such as flares and bottle throwing have occurred at games, and such actions will continue to not be tolerated as the season draws to a close.”