The Pension Protection Fund and Visteon UK scheme trustees have filed a $550m (£350m) claim against US Visteon Corporation to recover money for the fund.
Visteon Corporation said the claim with the US bankruptcy court could jeopardise its chapter 11 recovery plan as the UK pension fund claim is the largest single claim - with the next lowest being by Ford for about $200m.
Visteon Pension Action Group member Paul Bailey said the $550m figure refers to the full funding requirement of a closed fund in the UK.
However, in a court filing Visteon Corporation said under British law, its subsidiary Visteon UK has no present funding requirements.
The Pensions Regulator said: "We are aware of this situation but we cannot provide specific comment on individual cases. As with any investigation, we will consider any evidence presented to us."
The Visteon UK pension fund is currently in the PPF assessment period following the insolvency of Visteon UK in March last year when nearly 1000 workers at Basildon, Belfast, Enfield and Swansea lost jobs.
VPAG and union Unite said when the Ford plant in Swansea was taken over by Visteon in 2000, workers were assured their pensions would be safe but Ford broke "copper-bottomed promises" (PP Online, September 10, 2009).
VPAG called for Ford to take up the role of sponsoring employer to the UK pension fund and said this would be the "cheapest and easiest route Ford are obligated to take".
It added: "This would free Visteon to emerge from chapter 11 and also repay the money owed to Ford in the US. Ford could then claim - quite correctly - they have met their previous commitments and avoid UK legal action and negative publicity."