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Elizabeth Warren, the Democratic nominee in the hotly contested Massachusetts Senate race, worked on behalf of coal mining company in a bankruptcy case in the 90's. The company, LTV Steel, was fighting against a congressional requirement that it pay into a retired workers health care fund, an action required by the Coal Act of 1993.

The case, which was first reported by the Boston Globe, is the second past case to surface recently that could prove politically problematic for Warren, who polling shows is currently in a close race. Earlier this month it was reported that Warren, who is generally recognized as one of the top experts in the area of bankruptcy law, represented another corporate client. Traveler's Insurance, in 2009.

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Warren has offered an explanation for her work with both of these clients. In the case of her work with Traveler's Insurance, Warren worked with the company on a case where it was seeking protection against future claims, but part of the agreement reached in the case would have unlocked a $500 million settlement fund for asbestos victims. After Warren completed her work on the case however, that part of the agreement fell through when Traveler's won another case allowing it to avoid paying said victims. Warren said on Monday in a local radio interview that "the lower court made the wrong decision" with regards to that ruling.

In the case of her work with LTV Steel, Warren's campaign released a statement to the Boston Globe saying that the benefits of the company's retirees were not at stake in this case.

"Elizabeth is a bankruptcy expert and has fought for years for a strong bankruptcy system that makes sure retirees, employees, victims, and others can demand payment from insolvent companies and get a fair shake," Warren spokeswoman Alethea Harney said in the statement. "In the LTV steel case, there was never any question that coal miners and their surviving spouses would receive their full benefits under the Coal Act. This case involved bankruptcy principles and who would pay what into the fund."

Nevertheless, Warren's campaign has centered on her career of fighting for the so-called "little guy"- and so her representation of these corporations could appear to be, at least on the surface, at odds with that message. The challenge for Warren for the next six weeks will be to make sure that voters learn about the details of the cases.

ABC News currently rates the Massachusetts Senate race as a toss-up.