You can ask for only Singaporeans, but not Singaporeans and permanent residents.
You can welcome older workers, but not fresh graduates.
A list illustrating what is and isn't acceptable in job advertisements was put up on the website of Singapore's fair employment watchdog last week.
The Tripartite Alliance for Fair Employment Practices (Tafep) said it did this to provide greater clarity to employers and help them comply with existing guidelines on fair employment.
"During Tafep's regular engagement with employers and administrators of job portals, we have observed that there is a demand for clear and detailed advice on acceptable phrasing in job advertisements," said a spokesman.
The guidelines set out principles, but the list on Tafep's website has more detailed examples.
For instance, the guidelines state: "Words or phrases that exclude Singaporeans or indicate preference for non-Singaporeans should not be used in job advertisements."
This could be incorrectly interpreted to mean that as long as Singaporeans are among the workers preferred, the job ad is fine.
But as the list on Tafep's website makes clear, unacceptable phrases include "Singaporeans and Filipinos (or other nationalities)" and "Singaporeans and SPRs (Singapore permanent residents) only".
Bosses should also avoid stating preferences for age, race, language, gender, marital status and religion.
But they can say that a job is suitable for older workers, in support of efforts to improve job opportunities for this group.
Ms Wee Swee San, who handles job ads for restaurant Dan Ryan's Chicago Grill, said the examples were helpful as firms might not realise what phrasings count as problematic.
"We've heard about (fair hiring practices) on the news, but it wasn't so clear on what was allowed," she said. But publishers of ads, such as newspapers and job sites, also have a responsibility to advise advertisers, she added.
Ya Kun International executive chairman Adrin Loi noted that this was being done by some job ad platforms.
The move comes amid greater scrutiny of hiring practices.
Last month, the Ministry of Manpower (MOM) announced that it had taken action against 10 firms over discriminatory job ads.
In a Facebook post on Thursday, the MOM said it is investigating more ads that have been reported by the public.
The firms have been asked to take down the ads and their work pass privileges are being withheld while the ministry investigates, a process which is expected to take two weeks.
Acting Manpower Minister Tan Chuan-Jin shared the MOM's post on his own Facebook page, and added a call for civility as he referred to public responses to the job ads. "Be critical by all means, but be civil," he wrote.
"It is important to not stoke up hate and ill will as some are doing. It does no one any good. It does not reflect the kind of people we are nor the kind of society we aspire to be."