Thousands of supporters of former Prime Minister Thaksin Shinawatra seek to topple the government that itself came to power after mass demonstrations.
The tug of war is stranding tourists and raising fears of escalating violence. The military denies rumors of an imminent coup, while the king remains silent.
The antigovernment group swarmed the airport where the prime minister was supposed to arrive Wednesday.
Former Prime Minister Thaksin Shinawatra, facing corruption charges, fled to England this week. His absence may hurt the pro-Thaksin ruling party but also ease political strife.
Weeklong antigovernment rallies have raised concerns of a second coup in two years.
At issue are clauses that could shut down the popular former prime minister's party.
A May 10 poll could underscore how unpopular the regime is, as it slowly opens to foreign aid.
The majority coalition is expected to name a controversial prime minister.