I’m based in Scotland, company I work for is multinational but based/founded in America.

Pay increases relative to inflation have been an issue the last couple of years, with RPI being above 10% 2 years in a row now. Lots of asking will salary increases happen to meet that.

The company’s solution has been to offer a monthly “cost of living” bonus to our pay, BUT only to employees who are not in a union.

The email said anyon in a union/who joins one will not be eligible for this payment.
Basically wanted to know if this is legal?