A Queensland Senate candidate has called for laws to force publicly listed companies to seek written permission from the majority of their shareholders before giving support to "social activism campaigns", which he said threaten "to undermine our representative democracy and the national interest".

Family First candidate Rod McGarvie, who almost toppled former Labor Treasurer Wayne Swan at the 2013 federal election, abandoned the LNP in 2015 over the Abbott government's decision not to repeal section 18C of the Racial Discrimination Act and its softening on its same-sex marriage stance.

Telstra vowed to renew its "active position" on marriage equality, earning the ire of would-be senator Rod McGarvie. Credit:Louie Douvis

He has taken a hard line on those issues since and on Wednesday, released a "letter to the editor" bemoaning the "ominous trend" of the "rise of corporate activism" in the wake of Telstra renewing its active support of marriage equality.

That came after a public outcry following The Australian newspaper revealing the telco giant had quietly dropped its public support for the issue, following pressure from the Catholic Church, a major client.