Mayer Brown offices in Washington... Photo by Diego M. Radzinschi/THE NATIONAL LAW JOURNAL

The U.S. International Trade Commission will deliver its decision on whether domestic solar panel manufacturers have been injured by a surge in imports Friday morning, in what could be the first step toward President Donald Trump curbing trade in a multibillion-dollar industry.

However the commission rules, the trade case will be remarkable for the involvement of one law firm, Mayer Brown, which is now representing bankrupt U.S. solar company Suniva after years of fighting on behalf of Chinese and other foreign firms in similar proceedings.

In the arena of international trade law, where attorneys duke it out before quasi-judicial administrative agencies like the USITC and the Commerce Department over whether to slap tariffs on “unfair” imports, switching sides is unusual—if not unheard of. Firms usually either represent petitioning U.S. companies, or foreign exporter respondents, but rarely both.

Mayer Brown’s trade practice, by contrast, has shifted tack in a spectacular way. That’s in part because this is not an ordinary trade case. The matter before the USITC is what’s known as a Section 201 investigation, or a “global safeguard” proceeding. It could affect imports of solar panels and cells not just from one or two countries, but from all over the world. The last time trade was restrained under Section 201 was in 2002 in a case involving steel.

The other reason the shift is noteworthy is that Mayer Brown hasn’t simply started taking on petitioner-side cases—it’s taken on a massive petitioner-side case in the very same industry where it represented a Chinese respondent a little more than five years ago.

Chinese solar manufacturer Wuxi Suntech was Mayer Brown’s client in a controversial trade case brought in 2011 by SolarWorld Americas, which sought to hit solar cells imported from China with antidumping and countervailing duties. Those tariffs were ultimately imposed, but a loophole allowed Chinese companies to outsource some production and not be affected.

SolarWorld then brought another case with a wider scope targeting China and Taiwan, which was also successful. Suntech went into bankruptcy in 2013. Since then, Chinese investment in the solar industry has pushed out into other countries like Malaysia and Vietnam.

Now Mayer Brown and Suniva are fighting on the same side as SolarWorld, which also supports the Section 201 investigation. SolarWorld has been represented throughout by the firm Wiley Rein—a petitioner-side stalwart that has long fought for the U.S. steel industry.

But it’s more complicated than that. Suntech’s parent company —Hong Kong-listed Shunfeng International Clean Energy Limited, or SFCE—at one point was also the majority shareholder of Suniva, the Georgia-based solar cell manufacturer that Mayer Brown now represents.

After the firm filed the Section 201 petition in May, SFCE Chairman Yi Zhang wrote a letter to the U.S. International Trade Commission expressing “shock” that Mayer Brown was representing Suniva, saying it “clearly conflicted with the interests of its other client, Wuxi Suntech.”

He went on to request that the commission block the petition. The president of Suntech, Shuangquan He, wrote a nearly identical letter.

Mayer Brown partner Matthew McConkey, who is lead counsel for Suniva in the Section 201 case, responded with a letter of his own saying that not only was SFCE aware Mayer Brown was going to represent Suniva, Suntech—through its parent company—provided an “informed consent and waiver” of any potential conflict.

McConkey added that the letter from Suntech “should have no bearing on this matter.” The ITC investigation continued to move ahead.

A spokesman for Mayer Brown declined to comment for this story.

The Suniva matter is not the first trade case in which Mayer Brown has sided with a U.S. company instead of a foreign respondent; the firm has also represented U.S. Steel in trade proceedings. But it is a relatively new development for the firm’s trade group, which has deep connections in the administration and on Capitol Hill. Two former U.S. Trade Representatives, Susan Schwab and Michael “Mickey” Kantor, are at the firm.

The shift comes at a time when the political winds around free trade have changed dramatically with Trump’s election. Trump has repeatedly chastised companies for outsourcing and pledged to be aggressive in combating China’s trade practices. He terminated U.S. involvement in the Trans-Pacific Partnership trade deal and initiated a renegotiation of the North American Free Trade Agreement.

If the ITC determines on Friday that U.S. solar cell manufacturers were injured by a significant increase in imports, that will initiate the next phase of the case: coming up with a remedy. That could include tariffs or other policy mechanisms to restrain imports. The ITC will then make a recommendation to Trump by November, and he has wide discretion under the law about how to act on it. That has only increased uncertainty in the solar energy market.

“The Trump administration has made clear it wants to increase U.S. manufacturing and U.S. jobs,” said Wiley Rein partner Timothy Brightbill, the lead lawyer for SolarWorld, “and it’s willing to use not just the standard tools in the toolbox to try and accomplish that.”