Tariffs on steel and aluminum imports imposed by the Trump administration have workers in mills that use those raw materials to build other products concerned about the future of their jobs.

What's happening?

At the Borusan Mannesmann mill in Baytown, Texas, which manufactures steel pipe and tube products, workers penned letters to President Donald Trump on Tuesday, imploring the administration not to carry out the tariffs on steel and aluminum.

"We need this company to grow even more," Roger Jaime, a worker at the mill, told KHOU's Levi Ismail, as he and other workers wrote postcards to the White House and to other lawmakers to ask for relief.

Get Breaking News Delivered to Your Inbox

Why does it matter?

The workers are concerned that the tariffs will harm the company and potentially result in job losses. The threat has already waylaid Boursan Mannesmann's growth plans.

Just over 200 people work at the mill, which imports raw material from a facility in Turkey. But it could have more employees because the company has been planning a $75 million expansion that would have added 170 jobs. That investment has been put on hold in the wake of the steel tariffs, given that the cost of getting materials from abroad will increase and selling the more expensive finished products will likely get tougher.

Borusan Mannesmann administrators said the tariffs could create an added annual expense of more than $25 million for the relatively new company. Each employee's letter asks Washington to "please consider our situation" -- for more time to build and create the chance for the jobs Baytown needs.

What could the effects be?

Tariffs on steel and aluminum imports to the U.S. can help local producers of the metals by making foreign products more expensive. But they can also increase costs more broadly for U.S. manufacturers that cannot source all their needs locally and have to import the materials. That hurts those companies and can lead to higher consumer prices, economists say.

Steel and aluminum production jobs represent a small segment of the U.S. economy -- about 255,000 in steel and 61,000 in aluminum, according to Moody's Investors Service.

Manufacturers and end users make up a much larger portion of the economy. That means tariffs on raw materials, combined with retaliation from upset trading partners, may end up causing more harm than good. An estimate from consulting firm Trade Partnership forecast about 179,000 U.S. jobs lost versus 33,000 created as a result of the metal tariffs.

BMP, the parent company that owns the mill in Baytown, has filed an exclusion request with the U.S. government asking for an two-year exemption on raw material imports produced at its facility in Turkey -- which would otherwise be subject to a 25 percent tariff. The company argues in its request that the exclusion is necessary for its expansion and would "unlock" the investment the firm needs.

One of the projects Borusan Mannesman is contracted to supply is the GCX Pipeline, a roughly $1.8 billion, 514-mile project intended to transport natural gas from Texas' Permian basin to the Gulf Coast. The pipeline's owner, Kinder Morgan, also filed an exclusion request, specifically for the specialized X70 pipe. The company argues the materials cannot be obtained from U.S. suppliers in time to meet the project's October 2019 deadline.

Kinder Morgan (KMI) said the project "will directly support 2,500 well paying construction jobs during the eighteen months" required to complete it and that "steel pipe imports from Turkey are consistent with U.S. national security."

--CBS News' Jillian Harding and Rachel Layne contributed to this report