MPs have written to The Pensions Regulator (TPR) about its engagement with the Railways Pension Scheme (RPS) amid concerns over the scheme's future funding.
The Work and Pensions Committee (WPC) has questioned the watchdog after one of the UK's largest rail providers was disqualified from competitions over the future management of three major rail routes.
Stagecoach last week announced the Department for Transport (DfT) had excluded its proposals for the East Midlands, South Eastern and West Coast rail franchises because of "non-compliant bids principally in respect of pensions risk".
The company said TPR had estimated around £5bn to £6bn would be needed to plug the scheme's deficit, if no further support was granted by the government, but the rail industry had proposed £500m to £600m of payments.
Stagecoach chief executive Martin Griffiths said the private sector "should not be expected to accept material risks it cannot control and manage".
He added: "Forcing rail companies to take these risks could lead to the failure of more rail franchises and cannot be in the best long-term interests of either customers, employees, taxpayers or the investors the railway needs for it to prosper."
Now, in a short letter to TPR's new chief executive, Charles Counsell, who took on the role at the beginning of this month, the committee said the scheme's "substantial deficit" needs an "urgent solution".
It requested an outline of the extent of the deficit and TPR's past and planned actions related to this.
In a separate statement, WPC chairman Frank Field said: "While the staggering, parlous state of the RPS is anything but welcome, the one positive here is the clear signal from the government to industry of further, heavy consequences for so badly mismanaging a pension scheme.
"In the wake of Carillion, it is encouraging to see the government now taking public service provider pension schemes more seriously. We've written to TPR to see what they've done so far with this mess, and what the threat of further action by them can achieve to protect pensioners."
The scheme had not replied to a request for comment by the time of publication.
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