Dave Morris and Helen Steel petitioned Parliament on Thursday to allow them to appeal to the House of Lords, Britain's highest court, to overturn a ruling that they pay the hamburger chain $64,000 in damages, their supporters said in a statement.

The case, known widely in Britain as ``McLibel,'' resulted in a 314-day trial, the longest in English history. Now it could go on even longer. Morris and Steel said they were trying to defend the public's right to criticize companies whose business operations affect people's health and the environment. They argued that multinational corporations like McDonald's should no longer be allowed to sue for libel, the McLibel Support Campaign said.

The Oak Brook, Ill.-based McDonald's suffered an embarrassing public relations setback in March when an appeals court upheld the activists' claims that the chain sells heart-damaging food and treats its workers poorly. The court also did not dispute the original findings of a trial judge that McDonald's was responsible for animal cruelty and that it exploited children through its advertising.

The appeals court ultimately reduced the original damages award by $32,000, but upheld most of the libel verdict won by McDonald's against Morris and Steel.

The activists hope to persuade the House of Lords that they should have won their case against McDonald's outright.

If denied the opportunity to appeal to Parliament's upper house, Morris and Steel said would take the case to the European Court of Human Rights.