The Charity Commission says it has received "a number of complaints" about charities being involved in party politics in the pre-election period.
Andrew Hind, chief executive of the commission, warned charities recently about engaging in party political activity or leaving themselves open to the perception that they might be.
A commission spokeswoman said she could not say how many complaints had been received because of the way the information was recorded.
She added: "We will be reminding these charities, as all charities, to consider our guidance and ensure they follow its principles when making statements and comments."
Ben Summerskill, chief executive of Stonewall, was quoted saying the suggestion by shadow home secretary Chris Grayling that Christian bed and breakfast owners should be able to turn away gay couples was "very alarming to a lot of gay people who might have been thinking of voting Conservative".
The commission spokeswoman said: "We accept this could be perceived as party political. However, it could be open to interpretation." Summerskill said he stood by what he said.
John Appleby, chief economist at the King's Fund - a charity - said Tory plans for NHS savings amounted to "sleight of hand". He has since withdrawn the comment.