Mexican truckers have filed a lawsuit against the United States seeking $6 billion in compensation for losses they claim to have suffered since Washington banned them from crossing the border in violation of a trade pact, an attorney said Tuesday.

Mexico's National Cargo Transportation Association, or Canacar, filed the lawsuit representing 4,500 trucking companies, said Pedro Ojeda, the group's lawyer.

Ojeda said Canacar filed an arbitration notice with the U.S. State Department under the North American Free Trade Agreement in April.

"This is to demand equal treatment and reciprocity because our industry is suffering," Ojeda said.

The U.S. was required under NAFTA to grant Mexican trucks full access to its highways by January 2000, but opposition from U.S. labor unions and consumer groups led U.S. legislators to delay the opening until a pilot program allowing some trucks across was instituted in 2007.

The Teamsters union, U.S. consumer groups and independent insurers have warned that Mexican trucks are unsafe and lobbied Congress to keep them out. Many unions also voiced fears that U.S. drivers would lose work if lower-paid Mexican truckers were allowed to carry goods across the United States.

In March, President Barack Obama signed a spending bill that included a ban on spending for the pilot program. Mexico retaliated by imposing tariffs of 10 percent to 45 percent on dozens of U.S. exports ranging from fruit and wine to washing machines.

Obama has asked the office of the U.S. Trade Representative to work with the Department of Transportation, the State Department and Congress to create a new program.