* Two small fields would be affected
* About 190 workers could down tools
* Fields produced 46,000 bpd in 2013 (Adds detail and union, ExxomMobil comment)
OSLO, May 14 (Reuters) - A strike by Norwegian oil workers could shut two ExxonMobil fields in the North Sea next month if talks over pensions break down in mediation, labour union SAFE said on Wednesday.
About 190 ExxonMobil workers could down tools from June 16 at the Ringhorne and Balder fields if the company fails to give better pension terms for 31 workers, said Hilde-Marit Rysst, the head of SAFE.
"We hope that (ExxonMobil) gets the messages and takes action," Rysst said. "All the other operators have taken responsibility and made the necessary changes."
Talks between oil firms and two key unions broke down this month, raising the risk of a strike similar to that in 2012, when a 16-day strike across Norway's oil sector cut production by 13 percent and pushed oil prices above $100 a barrel.
The latest dispute would have a much smaller impact initially because the two ExxonMobil fields produced only 46,000 barrels per day (bpd) last year, a relatively small figure for both Norway and the company, but SAFE warned that the industrial action could be widened if necessary.
"It's definitely possible to escalate if we don't get a result," Rysst said.
Unions want ExxonMobil to grant a lower retirement age to 31 workers to bring them into line with other offshore employees, but the company said it would not discuss pensions.
"In our opinion and also in the opinion of the Norwegian Oil and Gas Association, this is a matter that doesn't belong in the negotiation or the mediation," ExxonMobil spokesman Knut Riple told Reuters.
The sides will appear before a state mediator in late May or in June and even if talks break down, leading to a strike, the Norwegian government has the right to impose a deal and force employees to return to work. (Reporting by Joachim Dagenborg and Balazs Koranyi; Editing by David Goodman)