Depends. Libertarians believe in free individuals making contracts. So unless the right to strike is somewhere included (here in germany it is through laws on a higher level) they would not, as strike is a breach of contract otherwise.

Why would the right to strike have to be in the contract? The contract just doesn't have to ban strikes, surely?

Libertarians default to liberty, unless opted out of, that's my understanding at least.

You make a contract which says you work for money.

If you strike, you do not work - you therefore break contract.

"libertarians default to liberty"

True. The liberty of individual. For example to make contracts - or to brake them. But the idea is, that society can only work if people do not break their contracts. Otherwise whats the point in them?

Surely then it depends upon the reason for the strike?

If the strike is over layoffs, wage cuts, unsafe work practices. They're all potential contract breaches.

"Surely then it depends upon the reason for the strike?"

For sure. If the other side breachs contract then, then strike is a very good way to fight that. Like work safe issues.

But layoffs for example ... are not really a breach of contract. (unless of course their contract was fir a longer time)

So we are back to the beginning again.

Libertarians aren't ideologically against strikes.

Well, if you define things like that, than I have to ask who do you mean by libertarians? There are many different branches.

I was refering to the free market libertarians and with strike I meant the ordinary one, like the one in question. Workers strike to get a better deal. Better money mostly and or less hours. And this is a breach of contract, which the free market libertarians I know, would be against.

The leftwing anarchist libertarians I know on the other hand would be all for strike and workers seizing the factory for themself.

I'm not sure there was a particular strike in question?!

You're right there are many varieties of libertarian. My understanding is that they are at least united in their small government ethos. With that in mind they would be against the levers of the state that could protect workers rights, and so be more likely to support systems that put those levers in the hands of individuals.

Also lets look at the US, they have fairly weak employment rights, you can be sacked without reason (as I understand it). Going on strike in that situation is functionally equivalent to handing in your notice and demanding that your employer reemploys you under a new contract. You are hoping that your value to your employer is still greater than the costs, if not he can just sack you and re employ someone else.

In that situation there isn't a breach of contract. I suppose you could argue semantically that that isn't a strike, but strikes (should) operate within the laws in force at the time, so I don't have a problem with the method of labour withdrawal changing to stay within these constraints.