No, there’s nothing preventing Labour from doing so. According to paragraph 18.44 of Erskine May;
By established convention, the Government always accedes to the demand from the Leader of the Opposition to allot a day for the discussion of a motion tabled by the official Opposition which, in the Government's view, would have the effect of testing the confidence of the House. In allotting a day for this purpose, the Government is entitled to have regard to the exigencies of its own business, but a reasonably early day is invariably found.
Even if the Government refused to adhere to this ‘established convention’, there is coincidentally an Opposition Day tomorrow (October 19th) during which Labour has control of the parliamentary time table under Standing Order 14. We’ll see if there’s a dramatic change of schedule allowed by the Speaker, but at the time of writing there are two opposition debates scheduled - one titled “Economic responsibility and a plan for growth”, and one on on the “Ban on Fracking for Shale Gas Bill”.
However, confidence votes tend to have the effect of rallying MPs of the governing party around the leadership - even if temporarily - see, for example, the motion of no confidence laid by Jeremy Corbyn in Theresa May’s government at the beginning of 2019.
Given that Conservative MPs currently seem to need no further encouragement to openly attack Truss’s premiership, but have not (yet) taken steps to remove her from the party leadership by changing the rules of the 1922 committee, it is unlikely that enough would openly vote against a Conservative government in the Commons. This is underlined by the fact that if a confidence vote did topple the government, and a general election were called, given the current polling many Conservative MPs would lose their jobs, and two extra years of an £84k salary is pretty hard to pass up. Even if certain MPs remain confident in retaining their seats, voting against the party leadership in a confidence vote is a sure-fire way to lose the party whip and be deselected, meaning they’d have to run as independents.