Bosses at the airport, which was bought by the Scottish Government for £1 in 2013, are still recruiting workers at the bare legal minimum.
First Minister Nicola Sturgeon previously urged Prestwick to raise wages after she was accused of "rank hypocrisy" over the issue.
The Scottish Government is a real living wage employer, but ministers say Prestwick is run at arm’s length.
Scottish Labour said the pay “makes a mockery of the SNP's non-existent commitment to fair work".
An advert for "aviation ground security officers" on a fixed-term basis for October stated they will be paid £8.91 per hour – the legal minimum for workers aged over 22.
A job profile said the role requires a "high degree of integrity" and "attention to detail", while officers "must be available around the clock”.
It said shifts can start as early as 4am and as late as midnight, with the work described as "physically challenging".
The real living wage, which is calculated by the Resolution Foundation think-tank and released each November, is currently £9.90.
It was £9.50 when Prestwick's job advert was promoted on social media.
The Scottish Government has long championed paying the real living wage.
After Prestwick came under fire over pay in 2018, Ms Sturgeon said: "Of course, Prestwick Airport is run at arm's length from the Scottish Government.
"But as I understand it Prestwick Airport is committed to the real living wage and is working towards having it paid to all those who work at the airport. The sooner it gets there, the better."
At the time, the airport said it had made a commitment "to pay our employees the Scottish living wage by April 2020".
Responding to the latest job advert, Scottish Labour's finance spokesman Daniel Johnson said: "This is deeply concerning news and makes a mockery of the SNP's non-existent commitment to fair work.
"Prestwick is controlled by the government – there is no reason at all for these workers to be being paid so poorly.
"It's time for the SNP government to fess up and pay workers properly."
A spokeswoman for Prestwick said: “Glasgow Prestwick Airport is proud to be a major employer in South Ayrshire, directly employing more than 250 staff.
“Despite the impact of Covid-19, in April 2021 the airport introduced a pay rate of £9.30 for fully trained staff with relevant experience.
"This was backdated by a year and based on the Scottish living wage from that time. The rate will be reviewed in April 2022.”
Asked how "relevant experience" is defined, the spokeswoman said: "As you may expect the security roles cover a variety of duties.
"This means recruits require extensive training, initially starting with classroom and practical training, then undergoing assessments for verification of competence. This process can take up to 12 months.
"Once confirmed as fully competent in all areas, they move onto the new hourly rate."
A Scottish Government spokesman said: "Glasgow Prestwick Airport is operated on a commercial basis and at arm’s length from the Scottish Government, in compliance with our obligations under the Trade and Co-operation Agreement between the UK and the EU.
"Ministers do not intervene in commercial decisions at the airport.”