Ashton, who has never held elected office and has very little international experience – she has been in her current job as EU trade commissioner for little over a year – is likely to face questioning from MEPs as to whether she is sufficiently qualified to become the EU's first full-time foreign minister.
Ashton rejected such claims in her inaugural press conference in Brussels last week, arguing that she had sufficient experience for EU leaders to unanimously back her and adding that she intended to show that she was the best person for the job.
However, MEPs are likely to be less forgiving in their scrutiny of Ashton, with some already saying that her approval is by no means guaranteed.
On Tuesday (24 November), Daniel Cohn-Bendit, co-president of the Green group, claimed in Strasbourg that it was "beyond comprehension" that EU leaders had given the high-profile job to an inexperienced commissioner who had "achieved nothing".
Still worse in Cohn-Bendit's eyes seemed to be her nationality. Coming from a country that has such a testy relationship with Europe, he claimed that Ashton would effectively have to "choose sides" in order to prove her credentials, either aligning herself firmly with the EU and thus risking problems in the UK, or adopting a typically British ambivalence towards the common European foreign policy, thus ensuring "she will have problems at the European Parliament".
UKIP accuses Ashton of Soviet funding
Meanwhile, the Eurosceptic United Kingdom Independence Party (UKIP) on Tuesday (24 November) sent a letter to European Commission President José Manuel Barroso claiming that Ashton, in her capacity as UK treasurer of the Campaign for Nuclear Disarmament (CND) in the early 1980s, knowingly accepted money from Soviet Russia.
UKIP MEP Gerard Batten said Ashton had either accepted the money knowingly or failed to realise that such donations were happening, making her "incompetent" and "negligent", he argued.
"Do you still believe that she is a fit and proper person to be in charge of the EU's (and Britain's) foreign and security policy?" Batten asked Barroso.
UKIP's accusations of Soviet influence come at a loaded time in EU politics. The centre-right European People's Party (EPP), currently the dominant force in the European Parliament, earlier this month said it would block the appointment of new commissioners if the nominees were seen to have been "associated with oppressive regimes".
A spokesperson for Commissioner Ashton, speaking to EurActiv, dismissed UKIP's accusations.
"Like many young people in the 1970s and early 1980s, Catherine Ashton was involved in the big campaign issue of the time with the Campaign for Nuclear Disarmament. She has never made a secret of that," the spokesperson said.
"This was more than 25 years ago. She left the CND in 1983 and has had no involvement in the organisation since then. During her time in the CND she never visited the Soviet Union, had no contacts with the Soviet Union and she never accepted any money from Soviet sources."
UKIP accusations 'laughable', says former colleague
A former colleague of Ashton's went a step further. Dan Smith, current secretary-general of London-based NGO International Alert, worked with Ashton at the CND in the 1980s, and told EurActiv that UKIP's accusations were "laughable" and "absurd".
Speaking to EurActiv from London, Smith said UKIP's accusation that the CND was "notoriously secretive about its sources of funding" is misguided, given that a large proportion of the NGO's revenue came from small donations at outdoor demonstrations across Europe in the 1980s. The accumulation of such small cash donations is impossible to trace, he said.
People are quick to forget that the CND was the largest mass movement in Europe at the time, he argued, accusing UKIP of "student politics" of the worst kind.
Smith noted that he was involved in a legal case over this same issue when the British Federation of Conservative Students made serious enough allegations about Soviet funding of the CND for him to sue for libel. They backed down, had to issue an apology and pay costs, he explained.
Commissioner Ashton will go before a hearing of the European Parliament next week in Brussels.