Well, they can furlough you even though your contract has a "no furlough" clause. They can increase the RJ flying above the contract max and decrease the mainline flying below the contract min. In essence, they can generally disregard the contract.....unless the union responds. Other than that, nothing.
Sorry to be so cynical in the previous post but I'm a little jaded with my recent experiences. Basically, what I've learned in my short time with a major is that it's a "zero sum" game, i.e., if that pilots gain in a negotiation, it comes at management's loss, and vice versa. The union works hard to gain concessions during any negotiation and there are tradeoffs with management. We'll concede that but we want this...etc. If the union negotiates a "no furlough" clause, for example, it comes at the expense of something else, i.e., a higher pay increase. There are varying degrees of union success across the different companies, and some companies aren't unionized at all. There are also varying degrees of "labor relations" across the different companies. SWA, for example, seems to have a great corporate atmosphere without a large union presence, however they lag the industry standard for pay. Important to note, though, is that they are making money and hiring, while the 'big boys" furlough and suffer losses. Each company and union is a little different. Set your sights on what you want and go for it. Just don't be surprised if reality sets in and things cool off for awhile. It's a business with a very small profit margin. When times are good, its great, when times aren't, it can be a little lean for awhile. Good luck!!