The Charity Commission has opened 16 cases involving charities alleged to have engaged in party political activity in the pre-election period.
The regulator revealed the figure last week after a request by Third Sector under the Freedom of Information Act. It said it received a total of 18 complaints during the purdah period between 6 April and 5 May.
"These included concerns that charities had not maintained their independence from political parties or had been perceived to be encouraging or providing support for a particular political party or candidate," the commission said.
Asked if the list included four charities already named in news stories, the commission said it did. But it declined to identify the other 12, claiming this would make them less willing to engage in "full and frank disclosure" and put them at risk of adverse publicity.
The commission said 10 of the cases were being dealt with by its Compliance Assessment Unit, which deals with serious matters, and the rest by other divisions. None had so far led to "an inquiry, investigation or otherwise", it said.
One recent complaint concerns Atlantic Bridge. Last October, the commission opened an inquiry into the charity, which aims to foster relations between the UK and the US, after earlier complaints that it was engaging in party political activity.
Liam Fox, the founder and a trustee of the charity, was appointed Secretary of State for Defence in the new government last week. The inquiry report will be published in due course.
The four charities confirmed by the commission are the health think tank the King's Fund, the gay rights charity Stonewall, the employment charity Tomorrow's People and the Tony Blair Africa Governance Initiative.
Senior staff at Stonewall and the King's Fund made apparently critical comments about the Conservatives; Debbie Scott, chief executive of Tomorrow's People, appeared in the Tory manifesto; and the Tony Blair Africa Governance Initiative is alleged to share its supporter database with the political campaigning website tonyblair4labour.org.
Third Sector has asked the commission to review its decision not to identify all the charities.