VANCOUVER -- Several unions are in B.C. Supreme Court in Vancouver Monday challenging a provincial law that restricts third-party advertising around provincial elections.

Under the law, known as Bill 42, third-party groups like unions can spend a maximum of $150,000 in the three months before a provincial election.

B.C. Teachers Federation president Irene Lanzinger says the law is an attack on free speech and democracy.

She says the law places no restrictions on the government but limits teachers, nurses and other members of the public service from speaking out about the effects of government policies.

Attorney General Wally Oppal has defended the advertising restrictions, saying allowing outside groups to spend as much as they'd like isn't fair to voters.

He says the idea is to keep the election focus on the candidates and political parties, instead of having third-party interests who may try to influence the outcome of the vote.