The strike affects 15 ports, and was called after the Swedish Dockworkers' Union was unable to reach an agreement with harbour owners over union representation.
“[The strike] is not something we want, but we haven't been able to find any other solution,” said Henrik Collvin from the Swedish Dockworkers' Union in Malmö.
Around 30 workers were present in the Malmö port from 7am on Wednesday, but Collvin said they didn't have high expectations of finding a solution soon.
The strike has also affected ports in Gävle, Helsingborg, Holmsund, Karlshamn, Malmö, Sundsvall, Söderhamn and Umeå, and will be extended to Stockholm and Gothenburg later in the day.
Employers have responded with a lockout, shutting out the affected workers from the workplace and meaning that around 1,000 dockworkers will not be working on Wednesday.
The union had wanted to establish a collective bargaining agreement for its 1,300 members with Ports of Sweden, in order to negotiate on issues such as working conditions. Currently dockworkers have a local agreement with the Swedish Transport Workers' Union, and the conflict has been ongoing since 2016.
Although the Ports of Sweden accepted a compromise put forward by mediators which would allow the Dockworkers' Union to have its own collective agreement, the union rejected it on the grounds that it would be excluded from local negotiations.
The 15 affected ports include some of the most important in the country, so the industrial action could have significant consequences for Swedish companies that rely on sending and receiving goods overseas.