OTTAWA -- A senior official in the federal labour program was told earlier this year that a federal ban on the use of replacement workers during strikes could potentially increase the frequency and duration of work stoppages, documents show.

Such a ban would have limited effect in federally regulated workplaces -- marine ports, airports, airlines and telecommunications companies, says a briefing note to the deputy minister of the labour program, the most senior official next to Labour Minister MaryAnn Mihychuk.

The federal labour code does not currently ban the use of replacement workers during a strike or lockout. Rather, it prevents their use in cases where their presence would undermine the union's bargaining position.

A 2011 internal government study found provincial bans on replacement workers in Quebec and British Columbia increased work stoppages by eight per cent in the service sector, with the exact opposite effect in the non-service sector.

When a work stoppage did occur, it lasted longer when there was a ban in place, the briefing note says.

Most federally regulated companies are in the service sector, such as banks and transport, and "it is likely that a ban on replacement workers would increase the possibility of a work stoppage," it adds.

The issue has fallen off the federal radar for the time being as the government looks at changes to labour rules concerning issues like flexible work hours and parental leave.

Hassan Yussuff, the president of the Canadian Labour Congress, said his group will push again for a ban on replacement workers when the time is right and they have the support of MPs.

"It's always on our agenda and it's always been a question of timing -- when do you put it up, and more importantly how much effort do you put into it," Yussuff said in an interview Friday.

"Every time we've done that, we've come close."

When that push does happen, it's likely to create friction between labour groups and employers in federally regulated industries.

"Employers would be uncomfortable with an environment where in the event of an unexpected work stoppage, they would not be able to continue the operations of their businesses," said Derrick Hynes, executive director of Fetco, which represents federally regulated employers.

The February briefing note, obtained by The Canadian Press under the Access to Information Act, was prepared ahead of an expected push by the federal New Democrats to press Parliament for a ban on replacement workers.

There have been 15 attempts in the last dozen years to enact rules that would prohibit federally regulated companies from hiring replacement workers in the event of a strike or lockout.

Each time, private member's bills from NDP, Bloc Quebecois, Liberal and Conservative MPs have failed to pass.

The briefing note recommends that changes to the Canada Labour Code on replacement workers should be handled by the three-way consultation process that includes the government, employers and labour representatives.