The exchange operator and regulation authority SIX Swiss Exchange said UBS issued two statements late last year that may have breached rules on how listed companies should release potentially price-sensitive facts that could significantly sway their share price.
A bank statement on October 30th 2012 titled "UBS announces strategic acceleration from a position of strength", which was released alongside its third quarter results, was being examined, the regulator said in a statement.
Another release, issued on December 19th 2012 with the title "UBS Board of Directors authorizes settlements of LIBOR-related claims with US and UK authorities; Swiss regulator to issue order", was also under investigation, it said.
That statement came amid the unfolding rigging scandal related to the Libor, a rate for lending between banks that also determines numerous financial and interest rate contracts around the world.
UBS was fined 1.4 billion Swiss francs ($1.5 billion) by US, British and Swiss authorities for its role in that market manipulation.
Thursday's probe, the regulator said, had been launched "on the grounds of possible breaches of the rules governing ad hoc publicity," which aim to ensure transparency and equal access to information for all actual and potential investors.
UBS reacted swiftly, issuing a statement that said there is "no basis" for the investigation.
"We take our disclosure responsibilities very seriously," the bank said, maintaining that in the two statements in question "we complied with all legal requirements."
It added: "Our disclosures to the market were also consistent with our own high standards for disclosure quality and timeliness."
Following the probe announcement, UBS saw its share price slip 0.63 percent in mid-morning trading to 18.81 francs a piece, as the Swiss stock exchange's main index remained flat.