Hello there. I confuse this sentences. It could be 'demanding the law to be passed' or 'demanding the law be passed'? Please explain to me.. Thanks
The first one is no good with the object. You can use these:

They are demanding (that) the law be passed
They are demanding to be served.
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Adding to Mr. MM's comment, it is important to note that "Demend" is among the group of verbs which take the subjunctive moods in American English. See below:
ask, demand, determine, insist, move, order, pray, prefer, recommend, regret, request, require, suggest, and wish.
The subjunctive mood dictates:

The verb immediately following the subjunctive verb must remain in its base form, i.e. I demend that John return my computer. Contrary to conventional grammar rule, the third person singular rule does not apply and here, the verb "return" doesn't need an "s".

I suggest that he come early to get a good seat. Not [he should come early], or [he comes early]
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The putative 'should' (I suggest that he should...) is an acceptable alternative to the subjunctive, Dimsum, especially in BrE. There is no violation of any '3rd person singular rule'; the fact is that the 3rd person singular form is unmarked in the subjunctive conjugation. And the word is spelt 'demand'.
Mister Micawber And the word is spelt 'demand'.
Of course!
Mister MicawberThe putative 'should' (I suggest that he should...) is an acceptable alternative to the subjunctive
Is this a common acceptance in American English? I ran into some people who consider the "putative should" an grammatical infraction. I understand in BrE it is ok.
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Yes, it is fine in any English. You 'ran into' a group of 'people'? Have you come up with any more reputable references? Leech & Svartvik, the first grammar I grabbed, says it 'occurs quite widely'.
Thank you so much Mister Micawber. I am understand now. It is about object. I am really respect for quick answer. Dimsum, thanks to you too that teach me about the subjuntive mood. It's the first time I knew the rules. I love for joining this website, Avangi. Thanks again.