"We'll first try to negotiate, but if there's no negotiation, the law of reciprocity will be put into practice," Lula said in an interview with Record TV, citing a law Congress recently passed giving the president powers to retaliate against trade barriers.
"If they're going to charge us 50, we'll charge them 50."
The president is unlikely to announce any retaliatory measures until the tariffs are implemented, said a Brazilian diplomat who requested anonymity to describe internal government debates.
"We have until August 1," the source said.
In a letter to Lula published on Wednesday, Trump linked the tariffs to Brazil's judiciary launching legal proceedings against former President Jair Bolsonaro, who is on trial on charges of plotting a coup to stop Lula from taking office in 2023 after hundreds of pro-Bolsonaro supporters stormed Congress. Trump said Bolsonaro was the victim of a "witch hunt."
Lula criticised Bolsonaro for perpetuating claims of legal persecution, stressing the former president's son, Eduardo Bolsonaro, took leave from his role in Congress at least in part to head a campaign in his father's favour in the United States.
"The former president of the Republic should take responsibility, because he is agreeing with Trump's taxation of Brazil. In fact, it was his son who went there to influence Trump's mind," Lula said.
In a social media post late on Thursday, Bolsonaro said Trump's letter announcing tariffs was received with "a sense of responsibility," adding he respects and admires the US government.
Bolsonaro argued the US measure was a reaction to Brazil's distancing from freedom. "This would never have happened under my government," he wrote.
The former president also urged the powers to act by presenting measures to restore what he called "institutional normality".
Lula said the government will set up a committee with Brazilian business leaders to "rethink" the country's commercial policy with the United States. He mentioned Brazil's new reciprocity law, passed just after Trump made his first tariff announcements in April, that allows the government to respond with reciprocal measures in case other countries impose unilateral barriers to Brazilian products.
Beyond imposing counter tariffs, the law would also allow Lula to restrict imports and investments and suspend intellectual property rights from US firms, among other measures.
The US is Brazil's second-largest trading partner after China and has a rare trade surplus with Latin America's largest economy.
Some market sectors, including aviation and banking, felt immediate pressure. Shares of some Brazilian firms declined on Thursday, with planemaker Embraer and major banks such as Itau Unibanco and Banco Santander posting losses.
But the tariffs could inflict pain in the US too, disrupting food prices, given Brazil's role as a major agricultural exporter of coffee, orange juice, sugar, beef, and ethanol. The proposed 50 per cent tariff would effectively halt the flow of Brazilian coffee to the US, its largest buyer, four trade sources told Reuters on Thursday.
Brazilian industry lobby groups representing sectors such as coffee and oil issued statements on Thursday, urging a diplomatic solution.
"We hope that diplomacy and balanced negotiations will prevail, despite ideologies and personal preferences, and that common sense will once again guide the relationship between these two great sovereign nations," Josue Gomes da Silva, the president of Sao Paulo industry group Fiesp, said in a statement.
