Scottish Labour conference after its leadership moved to block a vote on single market membership.
A group including former leader Kezia Dugdale had hoped to use a Brexit debate on Sunday to call for the UK to remain in the trading bloc.
But the party’s ruling body said the “situation regarding Brexit has changed significantly” in recent weeks.
It said the motions on single market membership were therefore out of date.
It has instead proposed a “unity motion” that does not mention the single market.
Pro-single market campaigners are furious, claiming the move was a “democratic outrage”.
If their motions had passed, they would have become official Scottish Labour policy – putting it at odds with UK leader Jeremy Corbyn.
Mr Corbyn insisted Labour was “absolutely not” clamping down on debate.
And the party’s Scottish leader, Richard Leonard, said delegates would be given a choice on whether to accept the Scottish Executive Committee’s ruling – although it would be extremely unusual for it to be overturned.
It comes as Mr Corbyn prepares to use his conference speech later on Friday to accuse the Tories of being deeply divided over Brexit.
Mr Corbyn recently said he now favours the UK remaining in a customs union after Brexit.
But he has stopped short of backing single market membership despite being urged to do so by many party members.
Pro-Europe delegates want to move a motion on Sunday voicing support for single market membership post-Brexit.
This motion – and several others from local party branches – will still be debated, but the chances are, they won’t come to a vote.
The party’s executive has put down a policy screed of their own (in such a last-minute fashion that it didn’t make it into the conference agendas handed out to delegates) which takes precedence over the others.
Crucially, members would have to vote this down before there would be any vote on the single market one.
This is possible, but seems unlikely – apparently the last time it happened, it was over the Iraq War. Fittingly, that was at conference in…Dundee
Former Scottish Labour chairman Jamie Glackin said a “healthy party” would encourage members to express their views even if they were at odds with the leadership.
He added: “Perhaps the reason it is not is that the days of control freakery in the Labour machine have not actually gone at all.
“Indeed, looking in from the outside of the party hierarchy, it does look like it has got significantly worse.”
Mr Leonard, who backs Mr Corbyn’s position on the single market, insisted that the party was not denying its members the right to vote on the issue.
He said delegates would be given a choice on whether or not to accept the executive’s decision, so the single market motions could still be debated on Sunday if there was enough support.
But he said the conference would also have the option of backing a “unifying position” put forward by the leadership that would keep the single market option open but “which doesn’t commit us at this point”.
The motion supports shadow Brexit secretary Sir Keir Starmer’s “six tests” for a deal to leave the EU – including whether it delivers the “exact same benefits” as being members of the single market and customs union.
for the next three days
Mr Leonard told the BBC’s Good Morning Scotland programme that it would be a “mistake” to “throw all our eggs in the basket of saying the Scottish Labour Party supports full membership of the single market” while Brexit negotiations were ongoing.
And he insisted that the option of a Norway-style agreement after Brexit was something that was “not entirely ruled out” by the party.
A new Scottish Labour for the Single Market group has been backed by Ms Dugdale as well as Edinburgh South MP Ian Murray and MEP Catherine Stihler.
In an article for the Labour List website, Ms Stihler argued that there was “no left-wing argument for leaving the single market” as membership helped to protect workers’ rights.
She added: “This is not, as some have ridiculously claimed, about factions within Labour. This is about protecting workers and consumers from the Tories, and that’s why Labour must do all it can to keep the UK in the single market.”
In his speech on Friday afternoon, Mr Corbyn will tell the conference that Labour is “alive and kicking” and a “party preparing to go into government”.
And he will accuse the Conservatives of forming a “divided government that has no clear idea of what it’s doing, what it wants, or where it’s going”.
He will add: “As Theresa May has now admitted, under her plans for a reckless Tory Brexit the UK risks losing access to European markets.
“Make no mistake about it, reduced access to European markets means fewer economic opportunities for people in the UK.”
SNP MSP George Adam said Labour was also “hopelessly split over Brexit”, and that the party leadership’s stance on the single market was “alienating huge numbers of Labour supporters and members across Scotland and the rest of the UK”.