The development follows the authorisation from Finnish Minister of Defence Antti Kaikkonen.
The parties will sign a strategic partnership agreement that will help in the development of a comprehensive solution for the security of the domestic ammunition supply.
The solution will affect the entire readiness condition and production of ammunition and explosives.
Additionally, the agreement will strengthen the partnership between the Finnish companies in the Nammo Group Partnership and the Defence Forces.
The agreement will be valid until stated otherwise or pending further notice.
Purchases made under the agreement are estimated to be worth around €20m annually and will not include the associated tax.
In 2014, a supply and partnership agreement was signed with the complete Nammo Group. The latest deal will consolidate this agreement.
Lapua and Vihtavuori are part of a Nordic ammunition group Nammo. Lapua focuses primarily on small calibre ammunition and produces cartridges and cartridge components for small arms.
According to Nammo, Vihtavuori manufactures gunpowder, a range of ammunition and infantry support systems.
Last month, the FDF Logistics Command signed a contract to procure night vision devices from local firm Senop.
In April, Estonia joined Finland and Latvia in a development programme that seeks to deliver an armoured vehicle platform.
The move came nearly four months after the three countries signed a letter of intent (LoI) to explore the possibility of jointly developing an armoured vehicle that will improve mobility.