Monday was supposed to be the deadline for anyone handing in their VAT and PAYE returns form, but the deadline has now been extended, after Skatteverket's website went down.
The deadline was first extended by two days and then later by one week from the time the website is back up and running and the electronic return forms are available again.
Tidsfristen för att lämna moms- och arbetsgivardeklaration förlängs också med 1 vecka från att e-tjänsterna fungerar igen.— Skatteverket (@Skatteverket) June 12, 2017
"What I've found out is that our tech staff managed to locate the problem on Sunday afternoon and are working on getting the site back," Skatteverket press officer Erik Lif Sjöcrona told digital news site IDG.
At 8am on Tuesday the website was still down. It will not be possible to apply for ID cards at their offices while the system is down, Skatteverket warned on Twitter.
It is not thought that the website blackout is caused by an act of external sabotage.
"We have not received any indications that it would be any kind of outside influence," Lif Sjöcrona told IDG.