It is understood Anchor has asked for tender documents from a number of agencies. It will then look to shortlist three for a potential pitch.
A spokesman for WCRS said the agency had not been put on notice by Anchor, and was unaware of any official review process.
Anchor is owned by the Scandinavian co-operative dairy giant Arla Foods, which also owns products including the Danish butter brand Lurpak, the flavoured milk drink Gulp!, the Harmonie Organic range, Cravendale PurFiltre milk and Rosenborg Blue Cheeses.
Anchor was brought back to television in 2001 after an absence of two years with a £7 million push through WCRS to promote the Anchor Spreadable brand.
Traditionally, Anchor's advertising has positioned the brand around its use of New Zealand free-roaming cows raised without chemicals.
WCRS has held the account since 1999, when it won the business from Saatchi & Saatchi, ending a 14-year relationship with the brand. The review was run by the AAR. Saatchis did not repitch because of a clash with Johnson & Johnson's Benecol, which is now handled by Miles Calcraft Briginshaw Duffy.
According to Taylor Nelson Sofres, the yellow fats market was worth £776 million last year, with the spreadable butter sector growing by 30 per cent, primarily due to Lurpak and Anchor.
BMP DDB handles Lurpak - whose advertising features the Aardman-created butterman, Douglas - and Cravendale accounts.