A source told PRWeek that while it was initially hoped that the deal would complete by the end of 2016, it is now more likely to be finalised in the spring.
Founded in 2004, Threepipe current and recent Threepipe clients have included restaurant chain Harvester, the UK's Food Standards Agency, the fruit company Dole, retailer TM Lewin and the NFL.
The agency has been increasing its digital and SEO capabilities recently, with the 2014 acquisition of Blowfish Digital, and the purchase of 12-person SEO agency Spot Digital this summer. At the time of the deal, the combined agency had 60 staff.
WE, which rebranded from Waggener Edstrom in September 2015, was listed at the world's 20th largest PR firm in the 2016 PRWeek Global Agency Business Report. Also an independent firm, 80 per cent of its $100m (£81m) revenue for 2015 was generated in the US.
It appointed former Edelman exec Alan VanderMolen in March to a new role overseeing its operations and growth plans in APAC and EMEA.
WE declined to comment.
Threepipe co-founder Jim Hawker said: "As a leading independent agency we are courted pretty regularly and we are friendly enough to speak to anyone that takes the time to get in touch. However, we are focusing on bedding in our own acquisition of a SEO agency from just a few months ago and that remains our focus for the foreseeable future."