Officials in Burma have lifted restrictions on election campaigning, pro-democracy leader Aung San Suu Kyi's political party said late on Monday.
This came just hours after the National League for Democracy (NLD) complained at a press conference that it was being denied the use of venues for rallies.
"It's a very significant change,'' spokesman Nyan Win told AFP news. ''We are still hoping for fair play."
There are 48 parliamentary seats being contested in the 1 April by-election.
Another NLD member told Reuters that the Union Election Commission (UEC) contacted the party to say that a ban on the use of sports grounds, which had prevented a rally planned for 14 February from taking place, was lifted.
Earlier, at the press conference in Rangoon, the NLD had warned that by-elections may not be fair because of the restrictions. Nyan Win told reporters that the party had been stopped from using three sports fields for the rallies.
The polls are being seen as a test of the government's commitment to reform.
The NLD boycotted Burma's last election in 2010 but agreed to rejoin the electoral process after the military-backed government brought in a series of democratic reforms.
Even if the NLD wins all 48 seats, the military-backed government would still have a commanding majority in parliament.
But, the BBC's Jonah Fisher in Bangkok says, an opposition victory would be seen as hugely symbolic.
Although insignificant in terms of numbers, the conduct of the election will go a long way towards deciding whether Western sanctions to Burma will be lifted.
The 2010 elections saw a military junta replaced with a nominally civilian government backed by the armed forces.
Since then, the new administration has embarked on a series of reforms, prompting the NLD to rejoin the political process.
Western nations have said that they will match progress on reform with movement on sanctions.
The NLD won a landslide victory in the 1990 election, but the ruling military junta at the time did not allow the party to take office.
Ms Suu Kyi, who won the Nobel Peace Prize, was under house arrest at the time. This is the first time that she has run for a parliamentary seat.