The Swiss economic affairs ministry said it had formally asked the US for "consultations" over tariffs of 25 percent on steel and 10 percent on aluminium.
Consultations constitute the first step in a full-blown legal challenge before the global trade body.
Switzerland, where the organisation is based, had on Monday "submitted a request for consultations with the US as part of WTO dispute settlement proceedings," the ministry said in a statement.
Several other WTO members, including the European Union, China, India, Mexico, Canada and Russia, are also fighting back against President Donald Trump's controversial trade policies.
Marking a departure from a decades-long US-led drive for free trade, Trump has justified the steep tariffs with claims that massive flows of imports to the United States threaten national security.
The tariff spat has escalated into an all-out trade war between the US and China.
According to Tuesday's statement, Switzerland exported steel and aluminium products to the United States last year to the tune of around 80 million Swiss francs ($80.7 million, €68.7 million).
"From Switzerland's point of view, the additional duties ... are unjustified," the ministry said, pointing out that Bern had contacted Washington when the tariffs were announced in March to request an exemption.
"The US has not responded to Switzerland's request for an exemption from the tariffs to date," the statement said, adding that the request for WTO consultations had been launched "in order to protect Switzerland's interests."
Bern did not mention possible retaliation, but other countries that have launched WTO challenges have warned they would slap tariffs on American products equivalent to the damage the US move was estimated to cause to their industries.
Under WTO rules, if 60 days pass without consultations resolving the dispute, Switzerland can ask the body to set up dispute panel, triggering a long and likely costly legal battle.