"Why Economists Are Wrong About Sweatshops and the Antisweatshop Movement"
John Miller
Challenge, Vol. 46, No. 1 (JANUARY-FEBRUARY 2003), pp. 93-122
Published by: M.E. Sharpe, Inc.
Article Stable URL: http://www.jstor.org/stable/40722184

Of interest, but only uses the word 'prostitutes' once.

The following implies that it's an obvious logical argument:

... For some activists the trafficking of women into the sex industry is morally wrong and exploitative because of its association with commercial sex, while for others forced prostitution is inseparable from global inequities of capital and labor that leave women in the global economy with few viable options aside from sweatshop labor or the typically more lucrative sex industry work.
[Soderlund, G. (2005). "Running from the rescuers: New U.S. crusades against sex trafficking and the rhetoric of abolition." NWSA Journal, 17(3), 64-87. Retrieved from http://muse.jhu.edu/journals/ff/summary/v017/17.3soderlund.html]

I think we're finally getting somewhere:

Hence, too, the often uncritical feminist embrace of a figure like New York Times columnist Nicholas Kristof, who rants and rages against the exploitation of female prostitutes halfway across the globe, even as he sings the praises of sweatshops. The faulty logic at work here—that closing sweatshops forces people into prostitution—not only problematically relies upon Kristof’s own moralizing determination that the sex industry unilaterally offers comparatively worse wages and working conditions than the sweatshop industry but also, incredibly, offers sweatshops as a solution to the problem of poverty driving many to work in any number of different capacities for very low wages in terrible conditions.
["Sex, Work, and the Feminist Erasure of Class"
Brooke Meredith Beloso
Signs, Vol. 38, No. 1 (Autumn 2012), pp. 47-70
Published by: The University of Chicago Press
Article DOI: 10.1086/665808
Article Stable URL: http://www.jstor.org/stable/10.1086/665808]

I finally found something. I put it in a new comment.