The police have previously been involved in violent clashes with the strikers A court in South Africa has barred police officers from joining a nationwide strike by public workers, which is in its ninth day.
A police spokeswoman said any officers who go on strike could face the sack.
More than one million teachers, healthcare workers and civil servants began their strike last Wednesday, in a dispute over pay.
South Africa's trade union federation, Cosatu, is holding nationwide marches on Thursday to further its demands.
These include a mass protest outside parliament in Cape Town.
The police sought the court injunction after the main police union announced that it wanted to join the strike.
Police and Prisons Civil Rights Union spokesman Norman Mampane said union lawyers would challenge the order, reports the AP news agency.
The police have previously been involved in violent clashes with some strikers and have fired rubber bullets, water cannon and tear gas at the protesters.
Last weekend, another court ordered the unions not to disrupt emergency services.
Military doctors have been deployed around the country to keep hospitals open.
The health ministry has asked for volunteers to help clean hospitals and cook food for patients.
The government has offered a 7% pay rise. Unions affiliated to Cosatu are demanding an increase of 8.6%.
The government says it cannot afford to deliver wage increases that amount to twice the rate of inflation.
On Friday, Health Minister Aaron Motsoaledi said hospital workers who interrupted vital medical care and forced colleagues to join the strike are carrying out actions tantamount to murder.
President Jacob Zuma has defended the unions' right to strike but also urged for them to end violence and intimidation.
This article is from the BBC News website. © British Broadcasting Corporation, The BBC is not responsible for the content of external internet sites.