The Zimbabwe president Emmerson Mnangagwa has said that his country is open for business, but this new law - the Zimbabwe Democracy and Economic Recovery Amendment Act - could scupper those plans as far as the U.S. is concerned.
MDC Alliance lawyers say they want the election results overturned, they say the inauguration must not happen and they say some of the evidence they have are vital poll papers, V11 forms, that show an attempt to tamper with figures.
The Constitutional Court now has 14 days to rule on the legal challenge by the Movement for Democratic Change (MDC).
Mr Mnangagwa won 50.8% of the vote compared with Mr Chamisa's 44.3%.More news: Redskins rookie RB Guice to miss season with torn ACL
The party is demanding either fresh elections or the instalment of their candidate Nelson Chamisa as president.
The party must prove that any irregularities were grave enough to change the outcome of the vote.
Judges must rule on the case within 14 days and could declare a victor, call another election, or order a run-off or recount, the Veritas legal group said. "We have a good case and cause".
Mnangagwa's inauguration planned for Sunday was postponed until the court makes its ruling.More news: Erdogan tells Turks to buy plunging lira as Trump turns the screws
The conduct of the election was largely deemed sound by worldwide monitors, but representatives of the European Union noted Mnangagwa benefited from an "un-level playing field" and some voter intimidation.
Judges have 14 days to rule on the case, and could declare a victor, call another election, or order a run-off or recount, according to the Veritas legal group. Mnangagwa's inauguration will take place 48 hours after the Constitutional Court announces its decision.
At least six people were killed in violence that erupted after the vote as security forces clashed with MDC supporters who alleged that Chamisa had been robbed of victory.
The aftermath of the polls has been marred by allegations by rights groups as well as by the MDC of a crackdown on opposition members, including beatings and arrests.More news: Jurgen Klopp reveals how Liverpool can challenge Man City for the title
Also on Friday, lawyers for senior opposition figure Tendai Biti asked judges to throw out charges against him over the protests against alleged election fraud, in a case raising further global concern about the new government.