Labour housing spokeswoman Mary Mulligan said there were 11,102 new houses completed in the first two quarters of 2008 - down from 12,996 for the same period last year.
And the number of housing association properties that were finished dropped from 1,878 in the first two quarters of 2007 to 1,292 in the first two quarters of this year.
Ms Mulligan said: "This clearly shows that the SNP's housing policies have set Scotland's house building programme into reverse.
"While the fall in completions in the private sector may be partly attributed to global credit conditions, the drop in the number of housing association properties is the direct result of the disastrous policies of the SNP government."
She said: "The chances of the SNP achieving their target of 35,000 new homes a year is drifting further away every day."
An aide to health secretary Nicola Sturgeon stated that ministers were "under no illusion about the serious challenges facing Scotland's housebuilders".