Two Oregon senators are challenging the U.S. Navy's plans to double its training operations off the Oregon Coast.

The Democrats, Ron Wyden and Jeff Merkley, sent a letter to the Navy this week saying they are concerned the training might damage the environment and coastal economy.

"Based on a number of comments we have received from a variety of interested stakeholders and constituents, we are concerned that many of the Navy's training proposals, including underwater minefield testing, explosive ordinance use, expanded land and air-based exercises, and widespread sonar training in particular, pose substantial environmental and economic risks," the senators wrote to Secretary of the Navy B.J. Penn.

The comment period on the Navy's plans to expand the Northwest Training Range Complex  ends Saturday. The proposed expansion would include exercises with guided missile submarines and unmanned aerial systems. The military also would implement new air and sea surface targets, new electronic signal emitters and development of a small-scale underwater training minefield.

The senator said they are particularly concerned about irreparable damage to fisheries and related industries, sonar impacts on marine mammals, impacts to endangered species and the potential release of hazardous materials into sensitive marine ecosystems.

The senators called on the Navy to reconsider whether it did a good enough job developing its scientific studies and methodology and to more fully explain potential environmental and cumulative impacts. They also asked the military to analyze reasonable alternatives and figure out ways not to do as much harm.