SolarWorld may have won another trade case, but it's not exactly happy.

Late last month, the Commerce Department issued a preliminary ruling in SolarWorld's anti-dumping case against Chinese solar producers. The government will slap large tariffs on Chinese suppliers, effective immediately, which could raise the price of modules shipped into the U.S. by up to 20 percent.

But rather than celebrate, SolarWorld is getting angry at the organization that represents the American solar industry.

Responding to an industry-wide call for a negotiated settlement to the solar trade war, SolarWorld President Mukesh Dulani penned an open letter to Solar Energy Industries Association President Rhone Resch this week, claiming that the organization is biased toward Chinese manufacturers. He called SEIA leadership "divisive" and said the organization encouraged some Chinese members to "break U.S. laws."

Although this isn't the first time SolarWorld has fired shots at SEIA, it is perhaps the most hostile. And it's also the first time SolarWorld has publicly declared its support for a diplomatic settlement with China -- assuming certain demands are met.

Below is the full letter from SolarWorld:

I am writing to address troubling comments and positions that you and SEIA have made and taken in regard to the anti-dumping and countervailing duty cases which SolarWorld has filed on behalf of U.S. solar manufacturers to counter the unfair trade practices of Chinese and Taiwanese solar manufacturers.

First, I wish to express my concern about SEIA’s decision to “condemn” the U.S. Department of Commerce’s recent preliminary determination on anti-dumping duties on solar imports from China and Taiwan. SEIA used this term twice in its media statement. To condemn the Commerce Department determination -- the ninth consecutive U.S. government finding of unfair trade practices by the Chinese solar industry -- is both inappropriate and wrong.

As SEIA is well aware, all countries and all industries are subject to international trade rules. Such rules ensure that nations and their producers do not create improper barriers to trade and use the false advantages of export dumping or illegal, export-oriented subsidies to prey on the producers of their trade partners. That you sanction the actions of some of your Chinese members to break U.S. laws and World Trade Organization rules raises serious questions about the interests and intentions of SEIA, a trade association that pledged in 2011 to remain neutral in this dispute.

I also want to affirm SolarWorld’s openness to alternative remedies in light of your ongoing calls for talks among the U.S. and Chinese governments, SolarWorld and China’s manufacturers. As you know, despite protestations from some Chinese manufacturers and their American allies to the contrary, SolarWorld has never closed the door on negotiations as long as they include two very basic conditions. First, any agreement or negotiated solution must eliminate China's unfair trade practices. Second, it must be enforceable. The Chinese manufacturers have yet to embrace these core conditions. Moreover, the Chinese record of compliance to suspension agreements hardly inspires confidence.

Lastly, based on our reading of the Commerce Department’s memo regarding the preliminary dumping and countervailing duties decisions, SolarWorld believes that there is a way forward toward a negotiated settlement. However, the SEIA proposal from September 2013 is not it. On top of its rejection by SolarWorld and other U.S. parties, the preliminary anti-dumping tariffs announced in the July 25 Commerce Department decision leaves little incentive for the Chinese manufacturers to source from Taiwan.

If SEIA wishes to reformulate and resubmit its proposal, I would gladly review it and respond. If we can discuss any new version before you leave for China starting Aug. 8, 2014, for your consultations with Chinese industry and government officials, I believe it would be useful.

It is my goal that both sides will pursue an amicable solution, and I request your support toward this end. In particular, I ask that you cease your improper, divisive rhetoric and advocacy of obsolete proposals, both of which can only thwart progress toward a viable and lasting agreement.

I look forward to your response.

Sincerely,

Mukesh Dulani

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SEIA said the letter was "surprising," given its work "behind the scenes to facilitate a meaningful, productive dialogue between SolarWorld and Chinese manufacturers."