The Scottish Premier League has decided to extend its season by four days - until 22 May - if Rangers reach the Uefa Cup final.
It has taken the unprecedented step of publishing two sets of fixtures for the final set of games.
Rangers' title rivals, Celtic, had already warned of their opposition to any extension to the season.
But the SPL insists that there was no alternative because of the number of postponed fixtures this season.
Secretary Iain Blair said: "It is well documented that this has been an exceptionally challenging season in terms of fixturing.
"The combination of a number of diverse circumstances has produced unparalleled scheduling problems."
"The outstanding fixtures cannot reasonably be played in the available time"
Celtic chief executive Peter Lawwell says that any extension would threaten the integrity of the competition.
St Mirren had also stated that they had booked a team holiday and would therefore oppose any change.
But, should Rangers beat Fiorentina to reach the Uefa Cup final, St Mirren will have to host the Glasgow outfit on Tuesday 20 May.
Dundee United chairman Eddie Thompson added that an extension would inconvenience his club's supporters.
"Our aim throughout has been to protect the integrity of the competition, balance the interests of our member clubs and have regard to player welfare and fixturing precedent," said Blair.
He described the proposal as "a modest extension to the season to enable Rangers FC to represent the SPL and all of Scottish football in the Uefa Cup final".
"It reflects the fact that the outstanding fixtures cannot reasonably be played in the available time and will involve some disruption for a number of our clubs," said Blair.
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Rangers face four games in eight days whichever fixture list becomes reality.
If Rangers make the Uefa Cup final on 14 May, the last round of fixtures for the top six clubs - which must be played at the same time on the same day - will take place on Thursday 22 May.
The Ibrox side will also travel to Motherwell on 17 May, while Gretna's hosting of Hearts will be moved forward to 8 May.
If Walter Smith's team lose to Fiorentina, who visit Ibrox for the first leg on Thursday, Rangers will travel to face St Mirren on 13 May then Motherwell two days later.
Rangers, who won the CIS Cup in March, meet Queen of the South in the Scottish Cup final on 24 May.
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