The business secretary, Vince Cable, has warned teachers, jobcentre workers and immigration officials who are preparing to take strike action on Thursday that there will be no public sympathy for walkouts.

Cable – who warned recently that tougher strike laws could follow walkouts – said: "I don't think the public will understand.

"The public view would be that we are negotiating and are willing to negotiate, so why would people be out on strike until that process has run its course?"

Up to 750,000 employees affiliated to the Association of Teachers and Lecturers, the National Union of Teachers, the University and College Union and the Public and Commercial Services Union are expected to stage Thursday walkouts over pension reforms.

Cable said he was "optimistic" that pensions reform talks would succeed, saying: "Most trade unions are committed to negotiations. They asked for the talks and we are taking them seriously."

He added that a "relatively" small number unions would strike on Thursday, without the backing of resounding ballot turnouts. "They don't have a very strong mandate," he said.

David Cameron confirmed during prime minister's questions that MPs would be subject to the pension reforms and will have to increase the amount they pay every month along with most other public sector workers. At the moment, to qualify for the most generous accrual rates MPs pay 11.7% of their salaries.

They are likely to have to increase this by five percentage points – the maximum increase the Treasury has indicated. On average, contributions will go up by 3.2 percentage points from next April, but those earning under £15,000 will be exempted and those earning less than £18,500 will be capped at a 1.5 percentage point increase.

Higher earners, including MPs, will have to pay up to five percentage points more to offset the cost of protecting low earners.

Cameron said: "In this house we are public sector workers as well, and we should be subject to exactly the same changes that we're asking others to take on.

"The increase in contributions should apply to the MPs system, even though it's a system where we already pay in quite a lot. We're saying [that] right across the board the increase in pension contributions is right to create a healthier long-term system."

And he added: "I don't believe there is any case for industrial action tomorrow, not least because talks are still ongoing. It is only a minority of unions who have taken the decision to go ahead and strike.

"What I want to see tomorrow is as many mums and dads as possible able to take their children to school. What I would say is this: what we are proposing is fair, it is fair to taxpayers but it is also fair to the public sector because we want to continue strong public sector pensions."

He also accused Labour of avoiding bringing up the issue of the strikes during because of the party's financial relationship with the unions.

"Twenty-six minutes into questions and not a squeak from the party opposition about strikes or pensions or the need for reform," he said. "Because they are paid for by the unions, they can't discuss the unions."