Workers at an ICT contractor marched out of their offices on Wednesday in protest at new terms and conditions that unions say amount to exploitation.
The employees walked out at 11am on Wednesday in a wildcat strike set to last until Friday evening.
"Our employer has brought in an inappropriate collective agreement for underpaid work and under the current conditions, even unpaid work," workplace representative Jenni Nieminen and shop steward Kalle Rantasuo said in a statement.
According to Trade Union Pro, Suomen Kotidata has been using the wrong collective agreement for years.
The company supplies ICT services for teleoperators including Telia and Elisa, and other big firms in Finland.
Under Finnish law most workplaces are covered by a collective agreement specific to their sector, but unions complain that some employers try to use the 'wrong' agreement in order to apply weaker conditions and lower pay.
"This is damaging collective agreement 'shopping', that weakens the conditions of ICT workers," said Mika Mäkelä from Pro. "The responsibility is with teleoperators and other commissioning companies in the sector, as well as Suomen Kotidata."
EDIT 26.7.2020 An earlier version of this story reported that Suomen Kotidata provides services for DNA. That claim came from the Pro trade union, but they have now corrected their statement.