Republican and Democratic lawmakers on Friday defended U.S. installers of rooftop solar panels and made an effort to beat back a pending decision that could make imported solar panels more expensive.

Bipartisan letters from 16 senators and 53 congressman were sent to International Trade Commission Chairman Rhonda Schmidtlein, and urged the agency to reject a petition by Chinese and German-owned companies that manufactured solar panels and cells in the U.S., but have since gone bankrupt.

The two foreign-owned companies that produced in the U.S. were seeking protection from imports that they say is hurting U.S.-based manufacturing. But the lawmakers wrote in their letters that imposing duties on these imports would only increase costs for domestic companies that install rooftop solar panels.

"Solar companies in our states believe the requested trade protection would double the price of solar panels," the Senate letter read. "Increasing costs will stop solar growth dead in its tracks, threatening tens of thousands of American workers in the solar industry and jeopardizing billions of dollars in investment in communities across the country."

Sens. Thom Tillis, R-N.C., and Martin Heinrich, D-N.M., spearheaded the letter writing campaign on the Senate side. Reps. Mark Sanford, R-S.C., Mike Thompson, D-Calif., Pat Meehan, R-Pa., and Matt Cartwright, D-Pa., did the same in the House of Representatives.

The letters were sent ahead of the trade commission's Aug. 15 hearing on the petition by Chinese-owned Suniva and German-owned Solar World. The ITC's role in the case is to decide if imports are hurting U.S.-based manufacturing, even if through the import of fairly traded goods.

The Solar Energy Industry Association, the main trade group for the U.S. solar industry, explained that the "agency is considering whether these two companies out of more than 8,000 across the U.S. solar industry deserve tariff relief that would impact the entire market." The group is opposing the companies' request at the agency.

Abigail Ross Hopper, president and CEO of the solar industry group, said the lawmakers effort shows that "trade tariffs are not a red or blue state issue."

She said if the agency approves new tariffs on solar panels and "these barriers are implemented, one of the fastest growing U.S. industries will be halted in its tracks." Thousands of American jobs and billions of dollars of private investment "will dry up," Hopper said.

The group said in a press release that the tariffs "would double solar prices, grinding growth to a halt and forcing 88,000 Americans — one-third of the U.S. solar workforce today — to lose their jobs just next year."

The solar energy industry has created 1 out of 50 new jobs within the U.S. in the last year, according to SEIA.