Yangon, Myanmar (CNN) -- Myanmar opposition leader Aung San Suu Kyi and other members of her party are delaying their parliamentary debut Monday as they seek to resolve a problem concerning the wording of the oath that lawmakers have to take.
Meanwhile, the European Union suspended most of the sanctions it had imposed on the country, citing the "transparent and credible" election that brought Suu Kyi to office and other reforms.
Suu Kyi and 42 other candidates from her party, the National League for Democracy, won seats in by-elections on April 1, a result welcomed by the United States and Britain as a sign of progress toward democracy in Myanmar after decades of repressive military rule.
After the elections, Suu Kyi and other newly elected opposition members were invited to attend the session of parliament this week in the capital, Naypidaw.
But they have requested that the wording of the swearing-in oath that lawmakers have to take be changed. The National League for Democracy asked the authorities to adjust the wording of the oath to say that parliamentarians will "abide by" the constitution rather than "protect" it.
"We want to change that constitution because it's not a democratic constitution," Ohn Kyaing, a spokesman for the party, said Sunday.
The constitution currently assigns 25% of parliamentary seats to unelected members of the military establishment.
Tin Oo, a senior party official, said that he believed the parliament would consider the issue Monday and that it could be decided upon this week.
The tension over the oath is the first sign of contention between the opposition and the reformist government of President Thein Sein since the by-elections.
Tin Oo said Thein Sein, who was visiting Japan over the weekend, had agreed before the elections to amend the oath.
"Whether Ms. Aung San Suu Kyi enters parliament or not is her decision," the president said Monday. "She has to decide it. The parliament is all in favor of her entrance and very welcoming of her."
United Nations Secretary-General Ban Ki-moon said Monday he will depart at the end of the week to visit the reclusive nation.
"Myanmar is only at the beginning of its transition," Ban told reporters. "Many challenges lie ahead. Many concerns have yet to be addressed. Yet I am convinced that we have an unprecedented opportunity to help the country advance toward a better future. That is why, today, I am announcing that I have accepted an invitation from President Thein Sein to visit Myanmar."
Ban has visited Myanmar twice before, in 2008 and 2009.
He said he looks forward to "personally congratulating" Sein and Suu Kyi on this trip. "Working together, they have come far," he said. "Working together, I am confident that they will go further still. And together, we will explore the many tangible and practical ways in which the U.N. can help."
The decision by the European Union to suspend most of its sanctions against Myanmar came Monday at the foreign ministers' meeting in Luxembourg. Only a ban on arms exports continues, according to the EU.
EU sanctions against Myanmar, first imposed in 1996, have included limits on diplomatic contacts and non-humanitarian aid and development programs, a freeze on the offshore accounts of Myanmar officials and visa restrictions.
Still, an expert stressed it will take time for the easing of sanctions to have any impact on those on the ground, living hand to mouth.
"On the day-to-day basis, nothing will change for the average person on the streets. These things take time. Manufacturing investment is what will drive this country forward," said Tony Picon, associate director at Colliers International, a real estate company.
One such person who might not feel change anytime soon is Ko Tin Lwin. He can earn up to $2 a day, or he can earn nothing, depending on whether he can find work when he shows up each day at the bustling Yangon port.
Lwin is one of hundreds of day laborers who carry cargo from docked ships to waiting trucks in Myanmar.
"I send 1,000 kyat ($1.20) a day back to my family in the countryside," Lwin said while waiting for another ship to arrive. "It only covers their food, nothing more, and I have to worry for tomorrow."
Myanmar's authoritarian military rulers have begun loosening their grip on power after decades in which dissent was stifled and freedoms severely limited.
In the past 12 months, the government has pardoned hundreds of political prisoners, secured a cease-fire with Karen rebels and agreed to negotiate with other ethnic rebel groups.
Myanmar's leaders have come a long way, but more work must be done, the EU said in the statement Monday. Relaxing sanctions are designed to encourage the country to continue, the organization said.
"These reforms will need time to implement and to bear fruit. The foundation for development is legitimate government, the rule of law and national reconciliation," the statement said. "The EU praises the peaceful nature of the process and the readiness of the parties to work towards the same goals, with a shared vision for political, social and economic reforms."
Western governments have applauded this month's by-elections and the other recent reforms by Thein Sein's government. The U.S. and Australian governments eased some sanctions on Myanmar last week.
While control of parliament will not change despite the opposition's strong performance, the result nonetheless gives the National League for Democracy a notable presence.
Myanmar's legislature has 664 seats, more than 80% of which are still held by lawmakers aligned with the military-backed ruling party, the Union Solidarity and Development Party.
Suu Kyi led her party to a landslide victory the previous time Myanmar held multiparty elections, in 1990. But the junta ignored the results and kept her under house arrest.
Released in November 2010, Suu Kyi was allowed to crisscross the country to rally support for her party in the elections.
CNN's Jethro Mullen and Kocha Olarn contributed to this report.