Ian Pearson said pay would be withheld where work was not done

In a letter to staff in all the government departments in Northern Ireland, Mr Pearson said there would be no increase to the 2003 pay award.

Thousands of civil servants have been taking part in a series of strikes in a protest over pay since late last year.

Staff are angry at not being awarded a cost of living pay increase.

"I support the right of staff to take lawful industrial action," said Mr Pearson.

"But whatever form that takes, it is also right to withhold pay where work is not being done."

A series of one-day strikes have been held across NI

Mr Pearson's comments follow industrial action by staff at the postal section of the Driver and Vehicle Licensing office in Coleraine, County Londonderry.

The action is likely to lead to delays in processing postal applications for car tax.

About 20 staff are taking part in a two week stoppage.

Drivers are advised to renew their motor tax at post offices, or at a local DVLNI offices, which are currently not affected.

Kieran Bannon of the trade union Nipsa said the strike would have a significant impact, as the Coleraine office dealt with a "heavy traffic" of postal licence applications.

"This is in addition to the massive queues you'll find at various local offices as well," he said.

"People will be likely going to local offices which are already very busy, so there will be considerable delays in getting them.

If there are mitigating circumstances we will take those into account Brendan Magee DVLNI

"Certainly, a backlog will develop within the Coleraine office."

In the past, the DoE has warned motorists they would be fined for not having car tax or unlicensed cars would be crushed.

However, the chief executive of the DVLNI, Brendan Magee, said they would listen to motorists who felt they had been treated unfairly.

"For anybody who's actually posted the documents in the post, clearly we'll be looking at those, as and when cases may arise, and if there are mitigating circumstances we will take those into account," he said.

Last week, the Department for Social Development said it would suspend without pay any staff member who took industrial action against the terms of their employment.

The warning came after Nipsa said the government must ensure the public does not suffer because of strike action by civil servants.

However, John Corey from the union denied department claims that it is holding customers to ransom.

Talks between Nipsa and management have so far failed to make progress.

The government has imposed a pay package which will add 3.67% to the wage bill of the Northern Ireland Civil Service.