The U.S. Supreme Court is expected to rule on the constitutionality of the Obama administration's health care overhaul law on Thursday -- the politically-charged legislation that could extend insurance coverage to at least 30 million Americans and has been President Barack Obama's signature legislative accomplishment.

After making three major rulings on Monday --including one reversing parts of the Arizona law cracking down on illegal immigration and another upholding the legality of its 2010 Citizens United decision -- the court announced it would sit again on Thursday to announce the rest of the opinions, SCOTUSblog reports.

The healthcare opinion will almost certainly be written by Supreme Court Justice John Roberts, according to the blog, which speculates Justice Anthony Kennedy may also contribute.

On Monday, the Supreme Court also threw out Americans ability to sentence juveniles to life in prison without the possibility of parole in a 5 to 4 decision. The ruling is in line with others the court has recently made, including one ruling out the death penalty for minors.

On healthcare, the court could strike down all of the law or invalidate only the requirement that most Americans purchase health insurance or face penalties -- the so-called individual mandate.

Other provisions of the law could be tossed along with the mandate. The Obama administration, as well as those challenging the law, have argued that if the mandate is rejected, related provisions requiring insurers to cover people with pre-existing conditions, and charge them the same rates as other policyholders, should also be invalidated because they would be too costly to uphold without the mandate.  

The justices may also overturn the law's expansion of Medicaid for the poor, which would reportedly extend insurance to 16 million people.