BOSTON (AP) — A bill freezing unemployment insurance rates for Massachusetts businesses has won final approval from lawmakers.

The House and Senate voted during informal sessions on Monday to send the rate freeze to Gov. Deval Patrick’s desk.

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The governor is expected to sign the measure, retroactive to Jan. 1, marking the fourth year in a row that the rates have remained unchanged.

The House and Senate have both also approved separate bills calling for an overhaul of the unemployment insurance system, but it’s not clear whether differences between the chambers can be resolved before the legislative session ends July 31.

Without the freeze, business groups had warned that employers would be facing a $500 million rate increase and that Massachusetts would be left with the nation’s highest unemployment insurance tax.