PRWeek understands that Aldi is particularly keen on firms to promote its food and baby products. The retailer did not specifically confirm or deny this.
An Aldi spokesperson said: "Aldi work with a number of agencies and regularly review the services we receive from external organisations. We are working with the [ad industry trade body] ISBA to identify PR and social media agencies that we may wish to add to our roster as Aldi continues to grow."
Weber Shandwick had held the account since 2008, and when Citypress was appointed the supermarket said that Weber remained its retained consumer PR and social media agency.
Weber had also previously handled Aldi's UK public affairs, until this account was won by Burson-Marsteller in 2014
Clarion has also worked with the supermarket for the past four years on consumer campaigns.
Aldi operates in 20 countries globally and in September it said it would invest £300m in its UK and Ireland stores, as it planned to extend its current 785 outlets to 1,000 by 2022. While rankings vary, it is often listed as the UK's sixth largest grocer.