A top US senator has moved to try to block George W Bush from refusing to enforce laws that he disagrees with.
Bush often adds "signing statements" to new laws
Arlen Specter, a Republican, proposed new legislation after the American Bar Association said the president's actions undermined the rule of law.
At issue are "signing statements", comments made by the president when he signs bills into law which set out how - or if - he plans to enforce them.
He has issued more signing statements than all his predecessors combined.
Among his most controversial were an assertion that he would not necessarily enforce a ban on torture - the McCain amendment - or a ban on the censoring of government scientists' findings.
Mr Bush has only vetoed one bill during his five and a half years in office, but opponents of signing statements say they amount to an illegal line-item veto of parts of bills he objects to.
"The president cannot use a signing statement to rewrite the words of a statute nor can the president use a signing statement to selectively nullify those provisions he does not like," Mr Specter said as he introduced his proposed law.
"The president cannot veto part of bill... he cannot veto certain provisions he does not like."
Mr Specter's proposed law would forbid courts from taking presidential signing statements into account when interpreting laws and would allow Congress to take the president to court over signing statements.
"If the president is permitted to re-write the bills that Congress passes and cherry-pick which provisions he likes and does not like, he subverts the constitutional process," Mr Specter, an increasingly frequent critic of the administration, said.
Experts said the bill had little chance of passage because the president's Republican party controls Congress.