President Donald Trump’s tariffs are hurting American businesses and could ultimately impact Republicans in the midterm elections, GOP Sen. Ron Johnson told CNBC Thursday.

The senator spoke with CNBC a day after sitting down with business leaders and farmers from Wisconsin. After the meeting, he sent a letter to Trump asking him to do everything in his power to “return certainty and stability to global markets.”

“The generalized steel tariffs are increasing their costs, making them uncompetitive globally as well as domestically,” Johnson said on “Power Lunch.”

“Farmers are losing access to markets they’ve been developing for decades. They’re losing orders.”

Johnson isn’t the only Republican to oppose Trump’s tariff policy. Many have argued it will damage both American consumers and businesses.

On Tuesday, key Republican Sen. Orrin Hatch, a Trump supporter and chairman of the Senate Finance Committee, threatened to push for legislation that will curb Trump’s trade authority.

"If the administration continues forward with its misguided and reckless reliance on tariffs, I will work to advance trade legislation to curtail presidential trade authority," the Utah Republican said on the Senate floor Tuesday. "I am discussing legislative options with colleagues both on and off the Finance Committee, and I will continue to do so."

The Trump administration has recently slapped tariffs on steel and aluminum imports, as well as a variety of Chinese goods. The actions prompted retaliatory measures from major trading partners.

Johnson said he hopes a lot of the pain caused by the tariffs is reversible.

However, “a lot of it is permanent damage,” he said. “They’re canceling or holding up their capital expenditures. Their competitors are able to raise prices, increase their profits.”

When asked if Trump's tariffs put Republican seats in Congress at risk, Johnson replied, “It does if it continues.”

He added, “I’d say somebody who has been put out of business because of his trade policies probably won’t vote for Republicans in the fall.”

— CNBC's Jacob Pramuk contributed to this report.