Partick Thistle will be playing SPL football next season after Inverness Caley Thistle lost out in their bid to ground-share with Aberdeen.
Thistle seem to have avoided relegation
Five SPL clubs voted against Caley Thistle's proposal, which would have allowed them to be promoted.
Partick Thistle, who would have been relegated if the move had gone ahead, had argued that Caley Thistle had failed to meet the SPL's criteria.
Inverness chairman Ken Mackie said: "We will be appealing."
He added: "At this time we do not know what the grounds are.
"I don't know the composition of the voting at all - all I know is that there were seven positive votes and I would like to say thank you to the clubs who voted in our favour.
"It is disappointing because we felt we had a good case and met all the criteria the SPL was asking for, so we thought we would move forward.
"But we were only one vote away, so we have to be positive and say it was close."
A statement from Partick Thistle expressed their delight at the decision.
"It is clear, however, that the confusion which has surrounded the outcome of the promotion/relegation issue has been damaging to the SPL, to all its members and to Scottish football in general," the statement on the club's website added.
"Partick Thistle will work with other members of the SPL to seek a resolution of these issues and to ensure that by the start of season 2004-05 there will be no doubts about the criteria which will apply for that season and the years to come."
Caley Thistle won the First Division on the final day
SPL clubs also agreed - unanimously - to reduce the SPL stadium seating criteria from 10,000 to 6,000 for the season after next, a matter that will be voted upon at the SPL's annual general meeting in July.
However, Partick joint manager Gerry Britton refused to accept that the matter was now closed.
"We'll see what happens," said Britton.
"I wouldn't be surprised if there was a few more twists and turns but it is
obviously great news so far for everyone involved with the club."
Aberdeen and Hearts have both backed Inverness' appeal, saying they believe the Scottish Football Association will overturn the SPL's decision.
Partick Thistle had threatened to take legal action if the SPL allowed Caley Thistle into the league.
They insisted that ground-sharing was contrary to the SPL's rules, while the Highland club's failure to put forward a stadium proposal by the 31 March deadline should also prohibit them from winning promotion.
It is the second successive season that the First Division champions have been denied promotion.
Last season, Falkirk failed to go up after their proposal to ground-share with Airdrie United was turned down.
The issue of ground-sharing arose as neither Inverness Caley Thistle's nor Falkirk's own stadia met the 10,000-seater criteria of the SPL.
That is a rule that is likely to be changed before the end of next season.