Overall, nearly 2 million vehicles were shipped to the US from Mexico in 2016 by all automakers, and that volume is expected to rise by 14.5% this year
Any change in U.S. tax policy that affected imports would have to be countered with a "mirror action" in Mexico, said Mexico's economy minister.
Trump's remarks came at the start of a meeting at the White House with union leaders.
"Great thing for the American worker," Trump said as he signed the order on his third full day in office.
Mexico has been exploring ways to lessen its dependence on the US out of fear that access to its No. 1 trade partner will be restricted by policies under Trump.
During a two-day meeting in Mexico City, the executives agreed to share data on trade, including the geographic areas where exports and imports have generated jobs
Trump said during the campaign that he'd impose tariffs of 35 percent on Mexican imports and 45 percent on Chinese imports to protect American jobs from unfair foreign competition.
"We're not really worried because tax incentives are just a one time kind of thing," responded ProMéxico's CEO to Trump's recent Carrier and Ford deals.
Bernie Sanders criticized the Carrier deal saying corporations can now threaten to send jobs abroad in exchange for tax benefits and incentives.
Trump set out plans on Monday that include withdrawing from TPP, which he calls a "potential disaster."