According to a report in Swiss weekly Le Matin Dimanche, Swedish defence firm Saab last year brought in US company Rockwell Collins to replace Roschi Rohde & Schwartz of Switzerland, which had originally been contracted to build the communications system.
While the Swiss would still be making their own encryption keys, the physical box and the software inside would be American made, according to the report.
Several experts quoted by the paper cautioned that the US company could potentially build a "backdoor" into the system, making it possible for US intelligence to see the information gathered during reconnaissance flights.
Following the trove of disclosures by former US intelligence contractor Edward Snowden of Washington's widespread spying efforts, the American firm's reported role raised eyebrows.
"With the Americans, it would be surprising if there were no back doors," Richard Morva, head of the Swiss Crows association that deals with electronic warfare, told the paper.
Christophe Darbellay, who heads Switzerland's Christian Democratic Party and who favours the fighter deal, said he wanted an explanation from Defence Minister Ueli Maurer.
"In the context of the Snowden revelations... I think this is a mistake. I will always have more faith in a (company from) Bern than in Uncle Sam," he told the paper.
When contacted by Le Matin Dimanche, both Saab and the Swiss defence ministry stressed that the deal had "never excluded the use of non-European components".
The most recent polls show that a majority of Swiss voters oppose the plan to buy the Swedish Gripen fighters, which would cost the Alpine country 3.1 billion Swiss francs ($3.5 billion, €2.6 billion).
Voters are set to cast their ballots on the issue on May 18th.
Supporters of the Gripen deal underline that in exchange for the sale, Saab and its engine supplier are contractually bound to sign business deals with Swiss firms worth 2.5 billion francs over the next decade.
On Friday for instance, Swiss aircraft maker Pilatus said it had signed a lucrative preliminary deal with Saab to deliver 20 of its training planes to Sweden and to create a joint software development centre in Switzerland if the Gripen deal goes through.