Transport union RMT has warned thousands of rail workers at FirstGroup face a financial hit totalling millions of pounds following the collapse in the company's share price this week.

The union called for the company's staff share schemes to be protected by the Government and claimed First Scotrail had already closed its scheme following the meltdown.

However, FirstGroup said it had not closed any of its share schemes, though the website was being remodelled. It "categorically" dismissed a claim by the RMT that the company faced being barred from bidding for future rail franchises, and said it had always marketed its schemes responsibly to employees, giving due warnings about share investment. "We are confident that in the long-term those levels will go back up," a spokesman said.

FirstGroup employs 13,000 people across its five rail franchises, but was unable to say how many were signed up to the share schemes.

It operates a buy-as-you-earn scheme where a salary deduction immediately buys shares at market price, and a sharesave scheme where the deductions went into an account with the option of converting to shares or withdrawing in cash.

RMT General Secretary Bob Crow said: "Thousands of frontline rail staff find themselves caught up in the chaos of the FirstGroup financial turmoil for doing nothing other than trying to save some of their hardearned wages. The union will be looking closely at the marketing and selling of these schemes to staff who now find themselves facing large financial losses."

Mr Crow said the union blamed a culture of mismanagement for the transport giant's credit rating coming under threat, prompting Monday's announcement of a suspended dividend and a rights issue to strengthen the balance sheet.

FirstGroup shares crashed by 30% on Monday from 223p to 155.6p, a 13-year low and one-fifth of their peak of 815p in 2007. The shares fell 7.2p to 127.4p yesterday. The proposed 85p-a-share three-for-two rights issue would dilute its theoretical ex-rights value to about 142p.

A FirstGroup spokesman said the developments were good news for staff because they would underpin the group's growth and future prosperity.

"There is always stock market volatility when you get this sort of event, but it is positive news for the long-term because it allows us to pay down some debt, invest in our businesses in the UK and North America and provide better bus and rail services in Scotland."