Halifax-based Irving Shipbuilding Inc. has been awarded a $500-million federal contract to carry out maintenance work for the Royal Canadian Navy.

The initial five-year contract guarantees a minimum of three Halifax-class frigates for the shipyard, with work planned to begin in the early 2020s.

The contract is expected to rise in value as additional work is added.

Public Services and Procurement Canada says the contract is expected to result in up to 400 jobs at the shipyard, plus hundreds of related jobs for marine sector suppliers and subcontractors across the country.

Last month, Ottawa awarded similar contracts to Seaspan Victoria Shipyards in British Columbia and the Davie shipyard in Levis, Que.

Overall, the federal government is spending more than $7.5 billion on the navy's 12 Halifax-class frigates to provide ongoing maintenance until they are retired in the early 2040s.

Irving is expected to begin construction of new warships for the navy in the early 2020s.

Of the current fleet of Halifax-class frigates, seven have their home port in Halifax, while five others are based in Esquimalt, B.C.

The Royal Canadian Navy requires that at least eight of the 12 frigates are able to deploy at all times in order to meet its commitments.