Northwest Pipe Co. announced that on May 11 the company received a staff determination letter from The NASDAQ Stock Market stating that, because the company did not file its quarterly Form 10-Q for the quarter ended September 30, 2009 and its annual report on Form 10-K for the year ended December 31, 2009, trading of the company's common stock will be suspended from The NASDAQ Global Select Market at the opening of business on May 20, 2010, and a Form 25-NSE will be filed with the Securities Exchange Commission, which would remove the Company's securities from listing and registration on the NASDAQ. Northwest Pipe attributed its failure to file to a previously disclosed ongoing internal investigation of certain accounting matters.