I often hear about measures that both major parties employ to prevent laws they do not like from passing, but in asking this question I would also like to know what a third party could potentially do to that end. Both in case of specific laws and all legislation in general.
So, assuming you mean: in Congress, before a bill is passed, how can a party prevent a bill from passing:
- Obviously, vote against it, on the full floor of either House
- Kill(vote against) or pigeonhole(take no action on) it in the Committee
- In the House of Representatives, in the Rules Committee, pass a restricting rule or schedule for a non-in-session date
Out of Congress, before a bill becomes law, obviously you have the Presidential Veto, which in the vast majority of cases kills the bill.