CHEONAN (Yonhap) -- The ruling Saenuri Party held a lawmakers' workshop Friday, marred by the absence of two presidential hopefuls apparently in anger after the party's leadership rebuffed their demand for changing the primary rules.

The two-day worshop in the central city of Cheonan was closely watched as intense debate was expected over the primary rule issue amid speculation that three minor contenders, Reps. Chung Mong-joon and Lee Jae-oh and Gyeonggi Province Governor Kim Moon-soo, could boycott the primary race en masse.

Both Chung and Lee did not attend the workshop apparently in protest after the party's leadership, comprising mainly of those loyal to their rival Park Geun-hye, rejected their demand the party first form a primary preparatory committee to discuss rule changes before launching a full-fledged election committee.

The three believe they stand little chance of beating former party chief Park and winning the party's ticket for December's presidential election without changing the current primary rules seen as favorable to her.

Under the current rules, the party's presidential candidate is determined based on a combination of votes, roughly half from party members and the other half from ordinary citizens. Minor contenders have called for determining the winner based entirely on votes from ordinary citizens.

Park and other members close to her have been against revising the primary regulations, saying it makes no sense to "adjust game rules to athletes" and that the "athletes" should adjust to the game rules.

Park consolidated her standing as a leading presidential hopeful after rebuilding the once-beleaguered party with sweeping reform measures and leading it to a widely unexpected victory in the April general elections.

But the rival camps escalated pressure on the party to agree to their demand.

"We won't back down even a little bit from our demand for an open primary," said Rep. Kim Yong-tae, a lawmaker close to the Gyeonggi governor. "Unless this is accepted, the primary under the existing system will fall through."

Earlier, Rep. Lee accused the pro-Park faction of taking the party in the wrong direction.

"They are trying to hold an easy primary," Lee said in a radio interview. "If they do this, would they be able to win the minds of the people in the main race?"

Meanwhile, the ruling party was also expected to discuss a set of reform measures that call for reducing privileges and benefits given to lawmakers and tightening their ethical standards, a move aimed at wooing voters ahead of the presidential vote.

On the table were six reform proposals the party suggested a day earlier, including scrapping lawmakers' immunity from arrest, reforming their retirement pension, banning lawmakers from concurrently serving in money-making jobs.