Bonnin, who earned US$112,504 a year in her role, alleges King would pressure her into having sex, going on "work trips" that had nothing to do with the business and to "drink excessive amounts of alcohol".
The civil suit claims King physically and sexually assaulted Bonnin, and that a senior supervisor knew about the inappropriate behaviour and reimbursed King for the cost of the trips and lunches.
"Fannie Mae promotes a culture that mistreats women, including hiring and paying them to have sex with upper management, and tolerates illegal, extreme, and abhorrent sexual harassment," the claim for damages states.
"King would verbally abuse plaintiff when she tried to socialise with other employees.
"He controlled every aspect of her day. Because of King's position at Fannie Mae, and her isolation from others, plaintiff feared losing her job if she did not co-operate with King's requests."
Bonnin claimed she was afraid of being fired if she didn't give into King's demands, but last year she got a protective court order against him.
King was fired soon after.
In an email statement to CNN, a Fannie Mae spokesman said the company had "zero tolerance for sexual misconduct and harassment".
"We investigate allegations whenever we are made aware of them, and we take swift and decisive action when we establish inappropriate behaviour," the statement read.