diff --git a/apis/v1alpha1/validation.go b/apis/v1alpha1/validation.go
index 9646919..10bb849 100644
--- a/apis/v1alpha1/validation.go
+++ b/apis/v1alpha1/validation.go
@@ -15,12 +15,22 @@
 package v1alpha1
 
 import (
+	"bufio"
 	"errors"
 	"fmt"
 	"net/mail"
 	"strings"
 )
 
+var (
+	defaultCLI              = "gcloud"
+	invalidCommandOperators = map[rune]struct{}{
+		'&': {},
+		'|': {},
+		'>': {},
+	}
+)
+
 // ValidateIAMRequest checks if the IAMRequest is valid.
 func ValidateIAMRequest(r *IAMRequest) (retErr error) {
 	for _, s := range r.ResourcePolicies {
@@ -57,3 +67,43 @@ func ValidateIAMRequest(r *IAMRequest) (retErr error) {
 	}
 	return
 }
+
+// ValidateCLIRequest checks if the CLIRequest is valid.
+func ValidateCLIRequest(r *CLIRequest) (retErr error) {
+	// Set default CLI
+	if r.CLI == "" {
+		r.CLI = defaultCLI
+	}
+	// TODO (#49): support other CLIs.
+	if r.CLI != defaultCLI {
+		retErr = errors.Join(retErr, fmt.Errorf("CLI %q is not supported", r.CLI))
+	}
+
+	// Check if the do commands are valid.
+	for _, c := range r.Do {
+		if err := checkCommand(c); err != nil {
+			retErr = errors.Join(retErr, fmt.Errorf("do command %q is not valid: %w", c, err))
+		}
+	}
+
+	// Check if the cleanup commands are valid.
+	for _, c := range r.Cleanup {
+		if err := checkCommand(c); err != nil {
+			retErr = errors.Join(retErr, fmt.Errorf("cleanup command %q is not valid: %w", c, err))
+		}
+	}
+	return retErr
+}
+
+func checkCommand(c string) (retErr error) {
+	scanner := bufio.NewScanner(strings.NewReader(c))
+	for row := 1; scanner.Scan(); row++ {
+		line := scanner.Text()
+		for col, r := range line {
+			if _, ok := invalidCommandOperators[r]; ok {
+				retErr = errors.Join(retErr, fmt.Errorf("disallowed command character %q at %d:%d", r, row, col))
+			}
+		}
+	}
+	return retErr
+}
diff --git a/apis/v1alpha1/validation_test.go b/apis/v1alpha1/validation_test.go
index f6302dd..9148900 100644
--- a/apis/v1alpha1/validation_test.go
+++ b/apis/v1alpha1/validation_test.go
@@ -200,3 +200,93 @@ func TestValidateIAMRequest(t *testing.T) {
 		})
 	}
 }
+
+func TestValidateCLIRequest(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name    string
+		request *CLIRequest
+		wantErr string
+	}{
+		{
+			name: "success",
+			request: &CLIRequest{
+				CLI: "gcloud",
+				Do: []string{
+					"run jobs execute my-job1",
+					"run jobs execute my-job2",
+				},
+				Cleanup: []string{
+					"run jobs executions delete my-execution1",
+					"run jobs executions delete my-execution2",
+				},
+			},
+		},
+		{
+			name: "success_with_default_cli",
+			request: &CLIRequest{
+				Do: []string{
+					"run jobs execute my-job1",
+					"run jobs execute my-job2",
+				},
+				Cleanup: []string{
+					"run jobs executions delete my-execution1",
+					"run jobs executions delete my-execution2",
+				},
+			},
+		},
+		{
+			name: "invalid_cli",
+			request: &CLIRequest{
+				CLI: "aws",
+				Do: []string{
+					"run jobs execute my-job",
+				},
+				Cleanup: []string{
+					"run jobs executions delete my-execution",
+				},
+			},
+			wantErr: `CLI "aws" is not supported`,
+		},
+		{
+			name: "invalid_do_command",
+			request: &CLIRequest{
+				Do: []string{
+					`run
+jobs execute my-job && rmdir dir`,
+				},
+				Cleanup: []string{
+					"run jobs executions delete my-execution",
+				},
+			},
+			wantErr: `disallowed command character '&' at 2:20
+disallowed command character '&' at 2:21`,
+		},
+		{
+			name: "invalid_cleanup_command",
+			request: &CLIRequest{
+				Do: []string{
+					"run jobs execute my-job",
+				},
+				Cleanup: []string{
+					"storage cat gs://bucket/secrets.txt > my-file.txt",
+				},
+			},
+			wantErr: `disallowed command character '>' at 1:36`,
+		},
+	}
+
+	for _, tc := range cases {
+		tc := tc
+
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			gotErr := ValidateCLIRequest(tc.request)
+			if diff := testutil.DiffErrString(gotErr, tc.wantErr); diff != "" {
+				t.Errorf("Process %s got unexpected error: %s", tc.name, diff)
+			}
+		})
+	}
+}