Macclesfield-based metal treatment firm Bodycote threw out an initial bid by the Swiss company, declaring it ‘unsolicited, conditional and unwelcome'.
Sulzer is understood to be weighing up its options, including a hostile bid.
Bodycote, which uses Financial Dynamics, seems set to vigorously defend itself, declaring initial interest from Sulzer to have ‘significantly undervalued the firm'.
FD is tasked with convincing shareholders to retain their investment as Bodycote defends its independence, although an improved offer could change its stance.
Bodycote shares have risen by nearly a third in the past six months, amid persistent bid rumours.
Sulzer is the world's second biggest pump-maker, but Maitland will have to counter concern in the North that an increasing number of local businesses are falling into foreign hands.
Glass-maker Pilkington, Manchester United, and holiday group MyTravel have been bought by foreign investors - the latter by Thomas Cook, which is owned by a German group.
Bodycote treats metals by putting them under intense weight and heat to improve durability. The result is harder-wearing material, used in high-stress applications such as jet engines and Formula One racing cars.