18 months in temp position, promised permanent but always denied. Any recourse?

My wife has been employed, through an employment agency, with the same company for the past 18 months. She was hired to fill a newly created position on a temp to hire basis. She has survived several permanent employee layoffs in a temp. position, and has taken on the responsibilities of these employees, but has not been hired to replace them. She has been passed around to various departments, in differing capacities; witnessed individuals hired into these departments with lesser qualifications, and still denied permanent employment. She has interviewed for several permanent positions, but is always told that the duties of her current temporary position must be met and therefore she is held back in this position as others are hired into full-time employment. She is regarded both locally and globally within her position as a part of the organization, as her responsibilities are integral to day to day operations. Her duties are not seasonal, or temporary; rather she is being handed duties once the responsibility of more than one permanent employee and denied the possibility of advancement based on the necessity of the continued completion of these duties. Her work ethic and merits have been spoken to by employees of the company, both verbally and written, so there is no question of capability or merit. She works for a global corporation with more than enough resources to provide permanent employment, as has been demonstrated over the months by continued expansion, yet has been continuously denied such.
Do we have a leg to stand on in substantive way?

Thanks
Kelson Treuhardt