Freedom of association is asserted in the 1974 Instrument of Government under chapter 2, article 1, section 5.

CIA World Factbook. Sweden https://www.cia.gov/the-world-factbook/countries/sweden/#government CONSTITUTION OF SWEDEN (1974). The Instrument of Government. https://www.equalrightstrust.org/ertdocumentbank/CONSTITUTION%20OF%20SWEDEN.pdf