By Nick Assinder BBC News Online political correspondent

Tony Blair will on Tuesday face a hostile reception from union members when he delivers an uncompromising speech to the TUC in Blackpool.

The prime minister is under attack on a number of fronts at the conference, which will be his most difficult since he became prime minister.

The unions are deeply opposed to military action against Iraq without clear evidence of a genuine threat from Saddam and full UN backing.

He will repeat his insistence that inaction is not an option

Many are still angry at the government's plans for the public services and the introduction of private firms into health and education.

There is the prospect of industrial action to protect pension rights in the wake of the crisis sparked by employers abandoning final salary schemes.

'Nuclear capability'

And rows over the euro and repeal of Tory anti-union laws will also feature high on the unions' agenda.

But Mr Blair is expected to give little ground over many of the key demands.

He has already made it plain he believes action against Saddam - in some form or another - is essential to stop him developing a nuclear capability which could threaten the world.

Left-wing union leaders are expected to be told to call off strike threats

He is expected to urge union members to consider the existing evidence of Saddam's attempts to build an arsenal of chemical, biological and nuclear weapons.

And he will repeat his insistence that inaction is not an option.

He will promise to set out more evidence in the long-awaited dossier detailing Saddam's capabilities.

11 September

He will pledge to build as wide an international coalition as possible against Iraq.

And he will repeat his insistence that the UN should be involved in any decision to act.

However, he will also warn that the UN must not shirk from flexing its muscles.

It must be ready to back action against Iraq, not be a way of delaying or fudging the issue.

It is expected that this will be a particularly personal and powerful part of his speech coming as it does on the eve of the anniversary of the 11 September attacks which led to the cancellation of last year's conference and the abandonment of his speech on that day.

Sound economy

Foreign affairs and the war against international terrorism are expected to take up around a third of his speech with the majority concentrating on domestic issues.

On the increasingly powerful demands for new rights for unions, the prime minister is ready to underline the advances that union members have already made under New Labour.

He will emphasise the creation of a sound economy with low interest rates and unemployment and the introduction of the minimum wage.

Many believe, with war looming, it would be impossible to run a proper pro-euro campaign in the foreseeable future

But he is also expected to tell left-wing leaders, led by Amicus's Derek Simpson, that there will be no return to the strike-ridden days of the 1970s.

He will offer his support over demands for secure pension schemes although he will oppose the idea of strikes over the issue.

Sensitive language

Once again he is expected to repeat his message that there is no option but to reform the public services.

He will urge the unions to do their bit to work with him on the reforms, rather than trying to block his plans.

And he will remind the conference of the huge amounts of money being poured into services like the NHS and education.

He will stress that that investment must go hand in and with wide-ranging reform.

Members will be particularly sensitive to the language he uses during this section of his speech.

Five tests

TUC General Secretary John Monks has already warned him not to repeat attacks over so-called "wreckers" and "forces of conservatism" which were widely seen as being aimed at some union members and left-wing Labour activists.

Eyes will also focus on whatever the prime minister has to say about the single currency.

The unions are split on whether he should hold a referendum on entry into the euro next year or postpone it until after the next general election.

Gordon Brown recently published more details of his five economic tests which was seen as putting further obstacles in the way of early entry.

Rough ride

And many believe, with war looming, it would be impossible to run a proper pro-euro campaign in the foreseeable future.

The prime minister's words on this issue will be trawled over with a fine tooth comb for any hints of his current thinking.

So, the prime minister is facing a rough ride when he addresses the TUC and - with the rise of left-wing leaders in many key unions - few expect him to be able to easily win over the conference.

But, inevitably, the threat of war and the fallout from the 11 September atrocity, which came at the start of last year's conference will hang over this meeting.

And, while domestic issues must be near the top of the prime minister's agenda, it is Iraq that is currently in his cross-hairs.