No. Any deductions other than income taxes and court-ordered payments require your written authorization. If you agreed in writing about the payment amount, that agreement is binding on both you and your employer, according to the state laws which govern written contracts. If you did not agree in writing, then the employer cannot make the deduction at all.
Borrowing money from one's employer, however, is generally a bad idea, for this very reason. Your only remedy, even though the employer has violated the law, is to go to a federal or state labor agency or to small claims court. Although you are legally protected if your employer attempts to retaliate against you, it still may place you in a very uncomfortable situation. After speaking with a government agency and/or a local attorney, you must make the determination whether it is worth it to challenge your employer, or to pay the money back more quickly, even though it imposes a financial hardship.