In the US, there are many possible sanctions
A frivolous case, or pattern of cases, can result in a number of punishments:
Paying the other side's legal fees -- Mind you, in the U.S, it is normal for each party to pay their own fees, and that will happen in "honest disagreement" type cases in which both parties have a valid perspective. "Loser pays" only happens when a) the loser has filed a ridiculous lawsuit, or greatly burdened the other side with frivolous filings; and b) the winner asks for fees.
Transferring other costs to the plaintiff as the court sees fit. Again, winner must ask.
Barring a plaintiff from filing future cases, without advance permission from the court. Again, winner must ask!
Barring attorneys or firms from practicing in certain areas of law.
Disbarment of the attorneys. That is decided by the state's Bar Association, typically a nonprofit trade association who in effect regulates lawyers in this manner.
For instance, California is one of only four states allowing cash awards for ADA violations. A clever person named Mr. Molski went around to different restaurants and checked their bathrooms for ADA compliance. If a toilet paper roll was 1/2" out of position from where ADA required, Molski would take notes. Molski checked dozens of restaurants every day, and passed these notes onto a San Francisco law office.
The law office filed hundreds if not thousands of these lawsuits against the various restaurants. The lawsuits all claimed that Molski was injured as a result of the ADA noncompliance.
Mind you, this was in the age before easy merging of databases and MS-Word documents. Since these hundreds of cases were so similar, they simply made Xerox copies of the relevant paperwork, only leaving a few fields blank to be typed in by hand. To reduce secretarial workload, they didn't bother customizing the date of injury: so all cases claimed Molski was injured on the same day.
Hundreds of defendants simply settled for amounts in the $5000 range (about half the cost of hiring a lawyer to grind through a trial). However, one defendant, a Chinese restaurant, fought. Their counsel discovered the hundreds of other same cases, and pointed out to the court that Molski was claiming to have suffered the same injury at dozens of restaurants on the same day. What an unlucky fellow!
The defendant then claimed Molski and attorneys were Vexatious Litigants, and the court wholeheartedly agreed.
- Molski was barred for life from filing any lawsuit without advance court approval (in which Molski would need to show a body of evidence to the court that yeah, a real and valid case was there).
- The law firm was barred for life from filing any ADA related cases.
- The law firm folded up, and is no more.
- The lawyers involved in the case quit practicing law.
Then we have Righthaven, who purchased from newspapers the "right to sue and collect damages" for copyright violations. Many bulletin boards, chatrooms, forums and Q&A sites allow/rely on "User Generated Content" (UGC), such as this here answer. They used search engines to find forums where users had copy-pasted newspaper articles. Generally, forums are protected from user behavior by the DMCA. Then, like Molski, they sued the forums, offering a settlement number below the cost of litigation itself. Again, hundreds paid; but a few fought on principle, with support from EFF. Again, Righthaven got destroyed in court - the right to sue cannot be sold. Courts ordered them to pay their victims' legal fees, bankrupting the operation.
Prenda tried a similar thing against people who BitTorrent porn.
I was in a case where we asked for fees. I got them, with such ease that I am kicking myself for not asking that the plaintiff be declared a vexatious litigant (which would have saved many others from this person). Further, the judge laid a heavy hint to the 3 other co-parties that if they asked for fees, they'd get them too. They did not ask.
Amusingly, one of the lawyers who should have asked, was unable to collect from the client. Should have asked...