UPDATE 1-Mexico's peso hits 9-month low on U.S. tax reform, inflation

(Adds background on peso weakness, tax reform, corruption)

MEXICO CITY, Dec 22 (Reuters) - Mexico's peso hit a nine-month low on Friday, battered by higher inflation, a potential threat to investment from tax reform in the United States, and corruption scandals that could help a leftist leading the race for the presidency.

The peso slumped to 19.6015 per dollar just before 11:00 a.m. local time, the lowest since March 15. The currency was still some way from the all-time lows it hit in January, just before U.S. President Donald Trump took office.

Trump's promise to rework the North American Free Trade Agreement (NAFTA) or tear it up, unless if provides more benefits to the United States, has weighed on the peso since last year, and analysts say that will continue to into 2018.

"I don't think we'll get to 20 before the end of the year, but probably in the first quarter, especially when the next round of NAFTA negotiations starts," said Banco Base analyst Gabriela Siller.

Inflation ticked up in the first half of December to 6.69 percent, above the 6.64 percent analysts had been expecting, keeping up pressure on the central bank to maintain high interest rates.

Persistent inflation and high interest rates are a toxic combination for President Enrique Pena Nieto's Institutional Revolutionary Party (PRI) heading into an election year, with Mexicans due to vote for a new leader in July.

To add to Mexico's woes, Trump signed a sweeping tax reform bill into law on Friday, slashing the U.S. corporate tax rate to 21 percent for 35 percent beginning January 1.

The bill has prompted worries in Mexico that the country could lose out on investment to its northern neighbor.

Analysts at CitiBanamex also pointed to a developing corruption scandal as one of the reasons for peso weakness.

On Wednesday, authorities arrested a former high-ranking official of the PRI, the latest in a string of damaging allegations to batter the centrist party.

The suspect in question, Alejandro Gutierrez, is accused of participating in a scheme to funnel taxpayer money into political campaigns in the state of Chihuahua.

The scandal could boost leftist presidential candidate Andres Manuel Lopez Obrador, who is running on an agenda to fight inequality and corruption and has an 11-percentage point lead over rivals, according to a recent survey by polling firm Parametria.

Some international investors are concerned about Lopez Obrador's potential stewardship of the economy, though the 64-year-old has tapped a respected U.S.-educated economist to lead his finance ministry if he wins the vote. (Editing by Dave Graham; Editing by Tom Brown)