Switzerland's Defense Ministry said Wednesday that any delay in the planned multibillion-dollar purchase of American-made F-35 fighter jets would have serious consequences for Switzerland's security after opponents succeeded in campaigning to put the purchase issue to a referendum, the AP reported.

The Swiss government announced Tuesday that campaigners broke the 100,000-signature bar on a petition calling for a referendum on the planned purchase of 36 Lockheed Martin-made jets as part of a major capacity upgrade of the Swiss air force by 2030.

Activists want the referendum to be held in March, the same month the U.S. proposal expires.

Opponents of the aircraft purchase argue that the fighter jets, which cost about $6 billion, are too expensive, tie Swiss security too closely to the United States and are ill-suited for Swiss needs. The Swiss Air Force mainly uses such fighters for air patrols in its European skies, not in conflicts abroad. Under the Swiss constitution, Switzerland is a neutral country, which limits its ability to engage in foreign conflicts.

In a statement Wednesday, the Swiss government noted that other Western countries, including Canada, Finland and Germany, have also opted for the F-35.

The Swiss government announced its choice of the F-35 last June after a comprehensive technical evaluation based on a cost-benefit analysis, and noted the technology, efficiency and extensive information provided to pilots in the cockpit.