Canada's revenue agency is feeling the pressure of Wednesday night's tax deadline.

As Canadians try to avoid the taxman's wrath by filing income tax returns before Wednesday's midnight deadline, those hoping to file on the Internet aren't having an easy time logging on. The online system appears to be overburdened, and there are reports that many people can't get onto the government's website at all.

Revenue Minister Gordon O'Connor says filers should be able to log on, if they keep trying.

"Well, (if) they just keep working at it, they'll get through," he said.

"(Canadians have) got until midnight and if you're an e-filer, as long as you don't owe us money you've got a full week."

O'Connor was referring to a reprieve of sorts for those experiencing delays with the online system -- a six-day extension to get their taxes done without facing a penalty. This year's Netfile income tax submission deadline is Tuesday, May 6 at midnight.

But those who owe money must send off their cheques by the April 30 deadline.

"We've always had a grace period," Canadian Revenue Agency spokesperson Peter Delis told CTV.ca on Wednesday. "The last couple of days we're usually inundated with people trying to access our site."

He said that many filers don't know about the grace period, which has been in place since the agency first introduced electronic filing in the late 1990s.

"We've always been quite flexible with that. In today's electronic world you have to be," he said.

Delis said users visiting the site should expect delays, but they should keep trying or just come back to the site later.

This should come as good news to some CTV.ca readers.

"I've been trying for three days to send -- no luck!" wrote Ruth in a comment posted on the website.

"I have now spent over two hours trying to do this," wrote a user named Mike.

Electronic filing has become the country's most popular way to submit tax returns. So far this year, the CRA has received more than 10.4 million electronic returns, about 500,000 more than were filed online at this time last year. Of those, about 3.3 million were filed by individuals using the Netfile system.

The revenue agency has received more than 6.3 million paper returns and almost 415,000 returns filed by telephone so far this year.

The last minute rush is par for the course for those working in the tax business, Delis told CTV.ca.

"It's kind of standard to experience slowdowns when you're dealing with heavy volumes," he said, noting the agency expects about 25 million returns. "We've received, as of a couple days ago, 17 million."

Those who file late will face a five-per-cent penalty, which doubles to 10 per cent for those who have filed late numerous times. Those who owe money after April 30 will be charged one to two per cent interest every month.

In 2006, about 3.6 million Canadians owed tax money to the government.

So far this year, the CRA has handed out more than 11 million refunds. This year's average refund has been about $1,400.

With files from The Canadian Press