ROME - MILAN'S La Scala opera house may be forced to cancel the opening shows of the season because of a strike by musicians protesting labour contracts, a union representing the workers said on Friday.

'We managed to come to an agreement about a document the management had signed, but other unions vetoed it and now we have to start all over again,' Mr Sandro Malatesta, local head of the Fials union told AFP.

The strike has been called by Fials, the trade union representing most of the theatre employees, including musicians, which objects to an agreement signed by La Scala management and three other unions in July.

The opera house management agreed the total benefits and wages package for 2008 to 2011 would be worth 11.5 million euros (S$22 million), but protesting employees said it was not enough.

Fials wants them to go on strike during the first three shows of the season, including the Dec 7 gala evening, which has been a tradition for the past 42 years.

In recent months, La Scala has cancelled a number of performances because of strike action.

At the end of November, the theatre abandoned the last three performances of Franz Lehar's The Merry Widow because of a strike by the same union.

Showings of Puccini's La Boheme were cancelled in July and Roland Petit's ballet La Dame aux Camelias was called off in October.

The gala opening has never been cancelled, and rehearsals for this year's Don Carlo, conducted by Daniele Gatti, have not been interrupted. -- AFP