Affleck is being sued for $2 million (£1.3 million) by Amanda White, a producer on his documentary I'm Still Here, which follows actor Joaquin Phoenix's attempts to launch a rap career.
In a new court submission, Affleck's attorney Marty Singer claims White refused to hand over important paperwork until her contract was finalised, describing her move as "extortionate".
Singer includes an email in which White appears to want to renegotiate her salary.
In the email to Affleck, dated 12 April (10), White allegedly writes, "I really feel that in good faith, the documents you refer to are my work product, so I would prefer to hold them in trust until we can get the matter of my deal resolved."
An attorney defending White claims the papers in question were "insignificant and not needed for months".
White filed her suit against Affleck earlier this month (Jul10) alleging she endured "uninvited and unwelcome sexual advances in the workplace" while making the movie. She reportedly joined the documentary in December 2008 and quit in April 2009, reports TMZ.com.