A controversial bill amending Kenya's election law has come into effect, which makes it more difficult for the Supreme Court to annul elections.
Uhuru Kenyatta won last week's re-run of the election, after the Supreme Court declared August's poll invalid.
President Kenyatta said on Monday that he did not agree with the new election law, however he did not send it back to parliament.
Opposition leader Raila Odinga pulled out of the re-run, calling it a "sham".
The Supreme Court said there had been "irregularities and illegalities" in the original poll, which was also won by Mr Kenyatta.
Mr Odinga said the necessary reforms had not been put in place before the re-run, which was boycotted by his supporters.
Mr Kenyatta won 98% of the vote in the re-run, with turnout at just under 39% - less than half that recorded in August's vote, according to the election commission.
Among the changes in the new law is a clause forbidding any court from invalidating election results for non-compliance with any laws, if this "did not substantially affect the result of the election".
When taking the unprecedented step to annul the August election, the Supreme Court did not make any mention of whether the overall outcome had been affected, but it said the correct procedures had not been followed.
Another change makes it possible for the head of the election commission - the IEBC - to be replaced by a deputy or another member of the commission if the position becomes vacant.
Just days before the re-run, IEBC chairperson Wafula Chebukati said he could not guarantee a credible vote, and criticised political parties for interference in the process.
A senior member of the IEBC also fled to the US in the days before the re-run, saying she had received death threats. Roselyn Akombe claimed the IEBC was under political "siege".
The amendments have been condemned by the opposition as well as Kenya's foreign allies.
Because Mr Kenyatta did not send the bill back to parliament within two weeks, it automatically became law.