Maxine Peake has backed an appeal to pay a £10,000 fixed penalty notice handed to a protest organiser angry about plans to cap NHS pay rises to 1%.
Mental health nurse Karen Reissmann, 61, was fined for breaching Covid rules at the rally in Manchester on Sunday.
Shameless and Dinner Ladies actor Peake urged people to "pay [the] NHS protest organiser's fine" via a crowdfunding page that has so far raised £14,000.
Greater Manchester Police (GMP) said the fine "appears appropriate".
Public gatherings are currently banned under coronavirus rules.
About 40 people attended the rally in Manchester city centre and GMP said most protesters dispersed after officers asked them to leave.
Assistant Chief Constable Nick Bailey defended the issuing of the fixed penalty notice.
"I absolutely recognise the tension in having to take any kind of action against health workers at this time, when we recognise the fantastic job they have played on the front line of the Covid response but I have a duty to ensure policing plays its role in reducing the spread of Covid," he said.
He said the enforcement action was issued "after a number of attempts to engage and encourage the protest not to take place".
"All fixed penalty notices are reviewed once they are submitted. However, the circumstances around this notice appears to be appropriate," he added.
A spokesperson for Greater Manchester Labour mayor Andy Burnham said: "Under current legislation protests are not permitted... and it is the responsibility of the police to uphold the law.
"But the mayor has asked GMP to review the full context of the situation and whether the fine was correctly and proportionally applied."
He added Mr Burnham "has given his unequivocal support for... NHS staff and opposes the insulting 1% pay rise offered by the government".
The BBC has tried to contact Ms Reissmann, who has thanked people on the GoFundMe crowdfunding page set up by actor Lamin Touray.
She said she was "overwhelmed by the amazing support" she had received, adding it was "heart-warming to know so many people support the right of us to safely protest the insulting 1% NHS pay offer".
Peake tweeted "pay for NHS protest organiser's £10k fine" and linked to the appeal from her official Twitter account.
Prime Minister Boris Johnson said the government was giving workers "as much as we can" in the "tough times" of the Covid pandemic.