Workers on Gina Rinehart's Roy Hill project are being paid a weekly bonus of $205 under contractual terms designed to deter them from taking unapproved industrial action.

The bonus, known as a ''project incentive payment'', has been included in the workplace agreements of at least two contracting companies working on the $US10 billion mine, port and rail project, and is believed to be involved in many more across the construction phase.

The AWU has helped to broker the incentive payments.

Amid speculation the project will be hard-pressed to deliver first ore on schedule in September 2015, the AWU has helped to broker the incentive payments, which can be forfeited by participating in strike action, according to documents lodged with the Fair Work Commission.

The identical clause appears in workplace agreements struck for Sydney-based company Diverse Tank Engineering, and construction company Neville Mallard, both of which are working on Roy Hill. It contains the following condition: ''In any week in which an employee engages in industrial activity not approved by the employer that ceases or disrupts operations, the payment will be forfeited in full.''