Found:

Subject Condition

SYNTAX: a Condition on Extraction Domain, stating the impossibility of extraction from subjects. EXAMPLE: this condition accounts for the ill-formedness of (i) and (ii), where who and what are extracted from the subject of the complement sentence.

(i)  *	I wonder who [IP [books of t] are on the table]
(ii) *	I wonder what [IP [reading t] would be boring]