Flexing its new constitutional muscle, Thailand's official anticorruption agency ruled today that the leading candidate for prime minister next month had engaged in financial wrongdoing that could disqualify him from holding office.

The candidate, Thaksin Shinawatra, said he would appeal the ruling to the Constitutional Court, a process that is highly likely to last past Election Day, Jan. 6.

If his appeal is rejected -- as all previous appeals to the court have been -- that could mean that the next prime minister would serve for just a short period before being banned from holding office for five years. That would leave politics in turmoil as the new Parliament struggles to form a working coalition.

The ruling is the strongest signal yet that Thailand is serious about reforming its corrupt political and electoral systems under a liberal Constitution that took effect three years ago. A separate Electoral Commission created by the Constitution is also asserting its power and has disqualified three parliamentary candidates for buying votes.