This paper examines a number of standard extraction tests which are applied to conditionals to determine their syntactic structure. The conclusion is that in conditionals where the protasis and the apodasis are 'linked' by the word then there exists an extra barrier to movement. I will speculate on the source of the extra barrier at the end of the paper, using data on the order of constituents in conditionals and the selection of conditional clauses.
Collins, Chris. 1998. A Note on Extraction from Conditionals. Cornell Working Papers in Linguistics 16, 57-66.