Tax advisers are being urged to file self-assessment tax returns as early as they can, as HM Revenue & Customs awaits the results of a union ballot that will decide whether staff will strike on the 31 January deadline.

Employees at HMRC, affiliated with the Public and Commercial Services Union, are voting whether to go ahead with the strike. The ballot closes on Wednesday.

The poll results will determine whether PCS members should call the strike to protest against government plans to close up to 250 HMRC offices and slash 25,000 jobs by 2011. The PCS expects 70,000 of its members to vote.

In a statement, HMRC said: ‘We will do everything we can to maintain our service to the public and business’ in the event of a strike, but encouraged taxpayers to file their returns early or use electronic filing to avoid any problems, should the strike go ahead.

In 2006, the PCS successfully organised a strike on the self-assessment deadline day after 60% of its members voted for the action.

HMRC managed to limit disruptions, however, by publicising which offices would be impacted by the strike.

This directed taxpayers to the nearest unaffected offices. In some cases managers stood outside closed offices to collect returns.

The department has not made any such contingency plans yet, as it is still awaiting the results of the PCS ballot, but insiders suggested that similar strategies to the ones used last year were likely to be implemented if the strike went ahead.

Financial secretary Jane Kennedy said she hopes the industrial action does not proceed but has expressed her confidence that HMRC would be able to cope with a strike if it takes place.

The PCS may have an unlikely ally in the event of strike action in the ICAEW, which has also expressed deep concerns with job cuts at the taxman.

Writing in this week’s Accountancy Age, ICAEW chief executive Michael Izza said: ‘It is hard to believe that any organisation ­ public or private sector ­ could survive cuts of 25,000 staff from a workforce of 94,000 without problems. If the HMRC is to deliver the service standards it aspires to it must be properly resourced.’

The possibility of a strike couldn’t come at a worse time for HMRC, as it continues to grapple with the fall-out of the missing discs crisis and the resignation of chairman Paul Gray.

The department is still bedding down the management restructuring implemented by acting chairman Dave Hartnett.

Internal surveys show that morale within HMRC is at a low ebb, with employees demoralised by massive job cuts and meagre pay increases.