Churches are charities and so are regulated by the Office of the Scottish Charity Regulator (OSCR).
During election periods campaigning activities are also covered by the Electoral Commission. Hustings are legitimate activities for churches during this period.
The Electoral Commission’s guidance on hosting a husting can be found at https://www.electoralcommission.org.uk/are-you-holding-a-hustings.
Charity law – Scotland: OSCR | Campaigning on political issues FAQs